Electrolytic capacitor and method of manufacturing the same

ABSTRACT

The present invention provides an electrolytic capacitor manufacturing method capable of manufacturing an electrolytic capacitor having the PTC function as easy as possible. A main electrode layer in a cathode is formed so as to have the PTC function. Different from a conventional electrolytic capacitor manufacturing method of connecting a PTC thermistor to a capacitor element to give the PTC function to an electrolytic capacitor so that an electrolytic capacitor manufacturing process is complicated and the number of manufacturing processes is increased by the amount corresponding to the PTC thermistor connecting process, the process of connecting the PTC thermistor to the capacitor element is unnecessary. Consequently, complication of the electrolytic capacitor manufacturing process and increase in the number of manufacturing processes caused by the PTC thermistor connecting process can be prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrolytic capacitor having asolid electrolyte layer and a method of manufacturing the same.

2. Description of the Related Art

In recent years, as one of electronic parts adapted for high frequencyapplications, an electrolytic capacitor is mounted on various electronicdevices. For example, under the circumstance that digitization,miniaturization and speedup of electronic devices is being acceleratedlyprogressed, larger capacity and lower impedance of an electrolyticcapacitor are demanded and, in addition, assurance of operationstability and operation reliability and longer life are also demanded.

A main part (capacitor element) of an electrolytic capacitor has, forexample, a stacked structure in which an anode made of a valve metal, anoxide film (dielectric layer) formed by anodizing the surface layer ofthe anode, an electrolyte layer, and a cathode are stacked in thisorder.

The electrolytic capacitors are roughly divided into two kinds accordingto the kind of the electrolyte layer; a liquid electrolytic capacitorwhose capacitor element includes an electrolyte layer (electrolyte) madeof a liquid material, and having a conductive mechanism mainly usingionic conduction, and a solid electrolytic capacitor whose capacitorelement includes an electrolyte layer (solid electrolyte layer) made ofa solid material such as complex salt or conductive high polymer, andhaving a conductive mechanism mainly using electron conduction. When thetwo kinds of electrolytic capacitors are compared with each other fromthe viewpoint of stability of operating characteristics, for example, inthe liquid electrolytic capacitor, the operating characteristicsdeteriorate with time due to leakage and evaporation of the electrolyte.In contrast, the deterioration with time in the operatingcharacteristics due to leakage and evaporation of the electrolyte doesnot occur in the solid electrolytic capacitor. Consequently, as anelectrolytic capacitor which can become the main stream in future,recently, in place of the liquid electrolytic capacitor, the solidelectrolytic capacitor is being actively researched and developed. Inthe research process on the solid electrolytic capacitor, for example,in consideration of a series of operating characteristics such as theleak current characteristic, impedance characteristic, and heatresistance, the main part of the solid electrolyte layer is rapidlyshifting from manganese dioxide or complex salt to a conductive highpolymer of a conjugated system.

For the solid electrolytic capacitor, in particular, based on thetechnical background to be described below, to prevent destruction(including firing and burning) caused by heat generated at the time ofshort circuit, the function of increasing resistance as the temperaturerises within a predetermined temperature range (so-called PTC (PositiveTemperature Coefficient) function) is in demand.

Specifically, the solid electrolytic capacitor is mounted on variouselectronic devices (electronic circuits) as described above and has anadvantage of generally low failure rate. However, when an overvoltage(voltage larger than rated voltage) or backward voltage (voltage whosesign of positive or negative is opposite) is applied due to a trouble onan electronic circuit and a dielectric layer is partially destroyed dueto the overvoltage or backward voltage, the anode, solid electrolytelayer, and cathode are unintentionally made conductive, so that shortcircuit occurs in the solid electrolytic capacitor. In the case whereshort circuit occurs, when excess current (short-circuit current) flowsin the solid electrolytic capacitor, the solid electrolytic capacitorgenerates heat and, in some cases, is destroyed by firing or burningcaused by the heat generation.

As a measure to prevent destruction caused by heat generated at the timeof short circuit in the solid electrolytic capacitor and also to preventdestruction of the solid electrolytic capacitor and circuit partsmounted on an electronic circuit, for example, a technique of mounting afuse on the solid electrolytic capacitor may be employed. A solidelectrolytic capacitor on which the fuse is mounted and having aconfiguration that a cathode and a cathode lead (lead for passingcurrent) are electrically connected to each other via the fuse is known.In a solid electrolytic capacitor of this kind, when the fuse is blowndue to heat generation at the time of short circuit, a circuit mechanismis interrupted, that is, a current path of excess current isinterrupted, so that destruction of the solid electrolytic capacitor isprevented. However, the solid electrolytic capacitor using the fuse hassome problems due to a structural factor and a mechanical factor of thefuse. First, when a fuse is mounted on a solid electrolytic capacitor,the structure of the solid electrolytic capacitor is complicated and isenlarged. Second, the mechanical strength of the fuse is low, that is,it is difficult to handle the fuse. When the process of manufacturingthe solid electrolytic capacitor is complicated, the manufacture yielddeteriorates. Third, in some cases, reliability of a solid electrolyticcapacitor on which a fuse is mounted is low. More concretely, forexample, when the periphery of a fuse is firmly covered with a moldresin, even if the fuse is blown due to heat generation at the time ofshort circuit, there is the possibility that the fuse is not completelyblown due to the existence of the mold resin, so that the circuitmechanism is not therefore interrupted and the solid electrolyticcapacitor may be destroyed. Therefore, a safety mechanism replacing thefuse is needed to increase the reliability of prevention of destructionof the solid electrolytic capacitors, and the PTC function as the safetymechanism is in demand.

Some modes of an electrolytic capacitor having the PTC function havebeen already proposed. Concretely, for example, an electrolyticcapacitor in which PTC thermistors are disposed so as to face acapacitor element, and the PTC thermistors and the capacitor element arecovered with a mold resin is known (refer to, for example, JapaneseUtility Model Laid-Open No. H05-006826). In the electrolytic capacitorof this kind, a PTC thermistor is not provided as a safety mechanismreplacing the fuse. As another example, an electrolytic capacitor havinga configuration in which an anode (internal terminal) of a capacitorelement and an anode lead (external terminal) are electrically connectedto each other via a PTC thermistor (semiconductor ceramic layer) isknown (refer to, for example, Japanese Utility Model Laid-Open No.H05-023529). Further, for example, an electrolytic capacitor having aconfiguration in which one of electrodes (external electrode) of acapacitor element and an electrode lead (metal terminal) areelectrically connected to each other via the PTC thermister (an excesscurrent/overheat protection device having the PTC function) is known(refer to, for example, Japanese Patent Laid-Open No. H11-176695).Generally, the PTC thermistor is electrically connected to a capacitorelement by thermo compression bonding or a conducive adhesive.

For a solid electrolytic capacitor having the PTC function, there arevarious demands from the following viewpoints.

In a process of manufacturing a solid electrolytic capacitor having thePTC function, to increase productivity of the solid electrolyticcapacitor, the solid electrolytic capacitor has to be manufactured aseasy as possible. However, the conventional solid electrolytic capacitormanufacturing method has the following problem. By using the PTCfunction of the PTC thermistor, destruction of the solid electrolyticcapacitor caused by heat generated at the time of short circuit isprevented. Since the PTC thermistor is connected to the capacitorelement to give the PTC function to the solid electrolytic capacitor,the solid electrolytic capacitor manufacturing process is complicatedand the number of manufacturing processes increases only by the amountcorresponding to the PTC thermistor connecting process required. As aresult, it is difficult to increase productivity of the electrolyticcapacitor. Therefore, to increase the productivity of the electrolyticcapacitor while preventing destruction caused by heat generated at thetime of short circuit by using the PTC function, it is an urgentnecessity to establish a technique capable of manufacturing the solidelectrolytic capacitor having the PTC function as easy as possible. Inparticular, in the case of establishing the technique capable ofmanufacturing the solid electrolytic capacitor having the PTC functionas easy as possible, it is also important to simplify the configurationof the solid electrolytic capacitor as much as possible in considerationof miniaturization of the solid electrolytic capacitor.

In the process of manufacturing the solid electrolytic capacitor havingthe PTC function, to assure productivity by increasing the manufactureyield of the solid electrolytic capacitor, it is necessary to stablymanufacture the solid electrolytic capacitor as much as possible. In theconventional solid electrolytic capacitor manufacturing method, however,for example, when a PTC thermistor is thermo-compression-bonded to thecapacitor element, the dielectric layer is easily damaged severely dueto a mechanical factor (excessive external force applied to thecapacitor element) at the time of thermo compression bonding, there isthe possibility that the solid electrolytic capacitor is mechanicallydestroyed during manufacture. Different from destruction of the solidelectrolytic capacitor caused by heat generated at the time of shortcircuit, the mechanical destruction of the solid electrolytic capacitoris fatal one and the basic structure itself of the solid electrolyticcapacitor is damaged. Therefore, the mechanical destruction cannot beprevented by using the PTC function. When the solid electrolyticcapacitor is mechanically destroyed during manufacture, naturally, themanufacture yield deteriorates and productivity of the solidelectrolytic capacitor cannot be assured, so that it becomes difficultto stably manufacture the solid electrolytic capacitor. Therefore, toincrease the productivity by increasing the manufacture yield of thesolid electrolytic capacity while preventing destruction caused by heatgenerated at the time of short circuit by using the PTC function, it isan urgent necessity to establish a technique capable of manufacturingthe solid electrolytic capacitor having the PTC function as stably aspossible. In particular, in the case of establishing the techniquecapable of manufacturing the solid electrolytic capacitor having the PTCfunction as stably as possible, as described above, it is also importantto manufacture the solid electrolytic capacitor as easily as possible inconsideration of productivity of the solid electrolytic capacitor.

Further, to achieve higher performance of the solid electrolyticcapacitor having the PTC function, it is necessary to reduce theresistance characteristic of the solid electrolytic capacitor as much aspossible. However, in the conventional solid electrolytic capacitormanufacturing method, the resistance characteristic is not sufficientlylow to improve the performance, so that there is room for improvementfrom the viewpoint of the resistance characteristic. More concretely,for example, in the case of connecting a PTC thermistor to a capacitorelement to give the PTC function to the solid electrolytic capacitor,the resistance characteristic of the solid electrolytic capacitorincreases only by the amount corresponding to the resistance of the PTCthermistor and the contact resistance between the PTC thermistor and thecapacitor element. The resistance characteristic can increase to thedegree that an adverse influence is given to the performance of thesolid electrolytic capacitor. In the case of bonding the PTC thermistorto the capacitor element by using a conductive adhesive to give the PTCfunction to the solid electrolytic capacitor, an amount of increase inthe resistance characteristic is often smaller than that in the case ofthermo-compression-bonding the PTC thermistor to the capacitor element.Consequently, from the viewpoint of preventing the resistancecharacteristic of the solid electrolytic capacitor from increasing, itis preferable to use the bonding method using the conductive adhesive.However, when increasing demand for higher performance of the solidelectrolytic capacitor is considered, it cannot be said that theresistance characteristic of the solid electrolytic capacitor obtainedin the case of using simply a conductive adhesive is sufficient.Therefore, to achieve higher performance of the solid electrolyticcapacitor while preventing destruction caused by heat generated at thetime of short circuit by using the PTC function, it is also an urgentnecessity to establish a technique capable of reducing the resistancecharacteristic of the solid electrolytic capacitor having the PTCfunction as much as possible.

SUMMARY OF THE INVENTION

The present invention has been achieved in consideration of suchproblems and its first object is to provide an electrolytic capacitormanufacturing method capable of manufacturing an electrolytic capacitorhaving a PTC function as easily as possible.

A second object of the invention is to provide an electrolytic capacitormanufacturing method capable of manufacturing an electrolytic capacitorhaving a PTC function as stably as possible by preventing theelectrolytic capacitor having the PTC function from being mechanicallydestroyed during manufacture.

A third object of the invention is to provide an electrolytic capacitormanufacturing method capable of reducing the resistance characteristicof an electrolytic capacitor having the PTC function as much aspossible.

A fourth object of the invention is to provide an electrolytic capacitorwhose PTC function is assured with the simplest configuration.

A fifth object of the invention is to provide an electrolytic capacitorcapable of preventing destruction caused by heat generated at the timeof short circuit by using the PTC function as much as possible.

A sixth object of the invention is to provide an electrolytic capacitorwhose PTC function is assured with lowest resistance.

An electrolytic capacitor according to a first aspect of the inventionhas a stacked structure in which a first electrode layer, a dielectriclayer, a solid electrolyte layer, and a second electrode layer in whichresistance increases in accordance with rise in temperature within apredetermined temperature range are stacked in this order.

In the electrolytic capacitor according to the first aspect of theinvention, the function of increasing the resistance in accordance withrise in temperature within a predetermined temperature range (so-calledPTC function) is given to the second electrode layer. Since the PTCfunction is assured without increasing the number of parts of theelectrolytic capacitor, the configuration of the electrolytic capacitorcan be prevented from becoming complicated to assure the PTC function.

An electrolytic capacitor according to a second aspect of the inventionincludes: a capacitor element having a stacked structure in which afirst electrode layer, a dielectric layer, a solid electrolyte layer,and a second electrode layer are stacked in this order; a resistancecontrol layer which is connected to the second electrode layer in thecapacitor element, has a sheet structure in which conductive particlesare held in a high polymer, and has a first face on the side close tothe second electrode layer and a second face on the side far from thesecond electrode layer, a surface process for exposing the conductiveparticles being performed on at least one of the first and second faces,and in which resistance increases in accordance with rise in temperaturein a predetermined temperature range; and an electrode lead connected tothe resistance control layer.

In the electrolytic capacitor according to the second aspect of theinvention, while assuring the function of increasing resistance inaccordance with rise in temperature within a predetermined temperaturerange (so-called PTC function) in the resistance control layer, thecontact resistance between the resistance control layer and the secondelectrode layer or electrode lead is reduced.

An electrolytic capacitor manufacturing method according to the firstaspect of the invention includes the step of forming a second electrodelayer in which resistance increases in accordance with rise intemperature within a predetermined temperature range on a solidelectrolyte layer in a stacked structure in which a first electrodelayer, a dielectric layer, and the solid electrolyte layer are stackedin this order.

In the electrolytic capacitor manufacturing method according to thefirst aspect of the invention, a second electrode layer is formed so asto have the function of increasing resistance in accordance with rise intemperature within a predetermined temperature range (so-called PTCfunction) on a solid electrolyte layer. Different from the case in whicha PTC thermistor is connected to a capacitor element to give the PTCfunction to an electrolytic capacitor so that the process ofmanufacturing the electrolytic capacitor is more complicated and thenumber of manufacturing processes increases by the amount correspondingto the PTC thermistor connecting process, the process of connecting thePTC thermistor to the capacitor element is unnecessary. Consequently,complication of the electrolytic capacitor manufacturing process andincrease in the number of manufacturing processes caused by the PTCthermistor connecting process is prevented. Moreover, to form the secondelectrode layer having the PTC function, it is sufficient to use, as thematerial of the second electrode layer, the materials capable ofassuring the PTC function in place of a material which cannot assure thePTC function. That is, since the electrolytic capacitor can bemanufactured by using the existing method of manufacturing anelectrolytic capacitor which does not have the PTC function only withthe change point of forming the second electrode layer by using thematerial for assuring the PTC function, the electrolytic capacitormanufacturing process is not complicated.

An electrolytic capacitor manufacturing method according to the secondaspect of the invention includes: a step of connecting a resistancecontrol layer having a sheet structure in which conductive particles areheld in a high polymer and whose resistance increases in accordance withrise in temperature within a predetermined temperature range to a secondelectrode layer in a capacitor element in which a first electrode layer,a dielectric layer, a solid electrolyte layer, and the second electrodelayer are stacked in this order; and a step of connecting an electrodelead to the resistance control layer, wherein the step of connecting theresistance control layer to the second electrode layer and the electrodelead comprises: a first step of performing surface process for exposingthe conductive particles on at least one of a first face facing thesecond electrode layer of the resistance control layer and a second faceon the side opposite to the first face; a second step of connecting theresistance control layer to the second electrode layer in the firstface; and a third step of connecting the resistance control layer to theelectrode lead in the second face.

In the electrolytic capacitor manufacturing method according to thesecond aspect of the invention, when a sheet-shaped resistance controllayer (high polymer, conductive particles) having the function ofincreasing resistance in accordance with rise in temperature within apredetermined temperature range (so-called PTC function) is connected tothe second electrode layer and the electrode lead, surface process forexposing the conductive particles is performed on at least one of firstand second faces of the resistance control layer. After that, the firstface of the processed resistance control layer is connected to thesecond electrode and the second face is connected to the electrode lead.Since the conductive particles are exposed in the resistance controllayer, the contact area (electric contact area) between the resistancecontrol layer (conductive particles) and the second electrode layer orelectrode lead increases. Consequently, the contact resistance betweenthe resistance control layer and the second electrode layer or electrodelead is reduced.

In particular, in the electrolytic capacitor according to the firstaspect of the invention, the second electrode layer has a stackedstructure in which two or more layers are stacked and, in at least oneof the two or more layers, resistance increases in accordance with risein temperature within a predetermined temperature range. Alternately,the second electrode layer may have a single-layer structure. In thecase where he second electrode layer has a stacked structure, the secondelectrode layer may have a two-layer structure including a mainelectrode layer for assuring conductivity and a sub electrode layerwhich is disposed between the main electrode layer and the solidelectrolyte layer and is used for electrically bonding the mainelectrode layer to the solid electrolyte layer. In this case, it ispreferable that the second electrode layer contains a high polymer andconductive particles held in the high polymer.

In the electrolytic capacitor according to the first aspect of theinvention, preferably, the second electrode layer contains at least oneof metal particles and conductive ceramic particles. In this manner, theresistance characteristic is lowered while assuring the PTC function inthe second electrode layer. In this case, the second electrode layer hasa stacked structure in which two or more layers are stacked and, in atleast one of the two or more layers, at least one of the metal particlesand the conductive ceramics particles is contained and resistanceincreases in accordance with rise in temperature within a predeterminedtemperature range. Alternately, the second electrode layer may have asingle-layer structure. In the case where the second electrode layer hasa stacked structure, it may have a three-layer structure comprising: amain electrode layer for assuring conductivity; a sub electrode layerwhich is disposed between the main electrode layer and the solidelectrolyte layer and is used for electrically bonding the mainelectrode layer to the solid electrolyte layer; and an auxiliaryelectrode layer which is disposed on the side opposite to the subelectrode layer while sandwiching the main electrode layer and containsat least one of the metal particles and the conductive ceramicparticles, and whose resistance increases in accordance with rise intemperature within a predetermined temperature range. Preferably, themetal particles are metal particles of at least one of the groupincluding nickel (Ni), copper (Cu), aluminum (Al), tungsten (W),molybdenum (Mo), zinc (Zn), cobalt (Co), platinum (Pt), gold (Au), andsilver (Ag), and the conductive ceramic particles are conductive ceramicparticles of at least one of the group including tungsten carbide (WC),titanium nitride (TiN), zirconium nitride (ZrN), titanium carbide (TiC),titanium boride (TiB₂), molybdenum silicide (MoSi₂), and tantalum boride(TaB₂). A material for increasing the resistance in accordance with risein the temperature within a predetermined temperature range is a liquidhigh polymer containing at least one of the metal particles and theconductive ceramic particles, and the second electrode layer may containa film-shaped high polymer formed by using the liquid high polymer andat least one of the metal particles and the conductive ceramic particlesheld in the film-shaped high polymer.

In the electrolytic capacitor according to the first aspect of theinvention, preferably, the second electrode layer is formed in a filmshape by using a liquid material for increasing resistance in accordancewith rise in temperature within a predetermined temperature range on thesurface of the solid electrolyte layer. With the configuration,destruction caused by heat generated at the time of short circuit isprevented by using the PTC function of the second electrode layer. Inthis case, the second electrode layer may have a stacked structure inwhich two or more layers are stacked and, in at least one of the two ormore layers, resistance may increase in accordance with rise intemperature within a predetermined temperature range. Alternately, thesecond electrode layer may have a single-layer structure. Preferably,the liquid material is a liquid high polymer containing conductiveparticles, and the second electrode layer contains a film-shaped highpolymer formed by using the liquid high polymer and the conductiveparticles held in the film-shaped high polymer.

Preferably, in the electrolytic capacitor according to the second aspectof the invention, at least one of a plasma process, an ultravioletprocess, an ozone process, and a laser process is performed as thesurface process on at least one of the first and second faces of theresistance control layer.

In the electrolytic capacitor manufacturing method according to thefirst aspect of the invention, it is preferable to form a secondelectrode layer so as to contain at least one of metal particles andconductive ceramic particles. With the configuration, when a secondelectrode layer is formed so as to have the PTC function, the secondelectrode layer is formed so as to contain at least one of the metalparticles and the conductive ceramic particles. Since the resistancecharacteristic of the electrolytic capacitor is reduced on the basis ofa low resistance characteristic of the metal particles or conductiveceramic particles, while preventing destruction of the electrolyticcapacitor caused by heat generated at the time of short circuit by usingthe PTC function, the resistance characteristic of the electrolyticcapacitor can be reduced.

In the electrolytic capacitor manufacturing method according to thefirst aspect of the invention, preferably, a second electrode layer isformed by supplying a liquid material for increasing resistance inaccordance with rise in temperature within a predetermined temperaturerange on the surface of the solid electrolyte layer. Consequently, atthe time of forming the second electrode layer so that the solidelectrolytic layer has the PTC function, a liquid material is suppliedon the surface of the solid electrolyte layer, thereby forming thesecond electrode layer. Different from the case where the dielectriclayer tends to be severely damaged due to a mechanical factor (excessiveexternal force applied to the electrolytic capacitor) which occurs atthe time of thermo-compression-bonding a PTC thermistor to theelectrolytic capacitor, a large external force is not applied to thedielectric layer during manufacture, so that damage due to themechanical factor during manufacture in the dielectric layer issuppressed.

The “liquid material” is a material which enters a liquid state (fluidstate) directly without using a solvent or indirectly by using a solvent(by being dissolved in a solvent) at room temperature (atmospheretemperature of normal environment in which, generally, a process ofmanufacturing an electrolytic capacitor is performed except forhigh-temperature environment which is intentionally set) and which canbe directly formed in a film by being supplied onto the surface of asolid electrolyte layer by using a method such as coating, dipping, orprinting. The “liquid state (fluid state)” is a concept including apaste state as long as the material can be supplied onto the surface ofa solid electrolyte layer and is, for example, a state where thematerial has a viscosity in a range from about 100 cP to 1,000,000 cP.The “liquid high polymer” is a high polymer having characteristicssimilar to those of the “liquid material” and is, concretely, thethermosetting high polymer or soluble thermoplastic high polymer (athermoplastic high polymer which does not directly enter a liquid stateat room temperature but indirectly becomes a liquid state since asolvent which can be dissolved at room temperature exists) except for aninsoluble thermoplastic high polymer (a thermoplastic high polymer whichdoes not directly enter a liquid state at room temperature and does notalso indirectly enter a liquid state since a solvent which can bedissolved at room temperature does not exist).

In the electrolytic capacitor according to the first aspect of theinvention, the function of increasing the resistance in accordance withrise in temperature within a predetermined temperature range (so-calledPTC function) is given to the second electrode without increasing thenumber of parts of the electrolytic capacitor, so that the PTC functioncan be assured with the simplest configuration. In this case, theresistance characteristic is reduced while assuring the PTC function inthe second electrode layer, the PTC function can be assured with thelowest resistance. Since destruction caused by heat generated at thetime of short circuit is suppressed by the PTC function, destructioncaused by heat at the time of short circuit can be prevented as much aspossible by using the PTC function.

In the electrolytic capacitor according to the second aspect of theinvention, while assuring the PTC function in the resistance controllayer, the contact resistance between the resistance control layer andthe second electrode layer or electrode lead is reduced. Thus, the PTCfunction can be assured with resistance as low as possible.

In the electrolytic capacitor manufacturing method according to thefirst aspect of the invention, a second electrode layer is formed so asto have the function of increasing resistance in accordance with rise intemperature within a predetermined temperature range (so-called PTCfunction) on a solid electrolyte layer. Consequently, complication ofthe electrolytic capacitor manufacturing process and increase in thenumber of manufacturing processes caused by the PTC thermistorconnecting process is prevented and an electrolytic capacitor can bemanufactured by using the existing method of manufacturing anelectrolytic capacitor which does not have the PTC function, theelectrolytic capacitor having the PTC function can be manufactured aseasily as possible. In this case, at the time of forming the secondelectrode layer so as to have the PTC function, the second electrodelayer is formed so as to contain at least one of metal particles andconductive ceramic particles. Consequently, because of the lowresistance characteristic of the metal particles or conductive ceramicparticles, the resistance characteristic of the electrolytic capacitoris reduced. Thus, the resistance characteristic of the electrolyticcapacitor having the PTC function can be reduced as much as possible. Atthe time of forming the second electrode layer so as to have the PTCfunction, a liquid material is supplied on the surface of the solidelectrolyte layer, thereby forming the second electrode layer.Consequently, destruction in the dielectric layer due to a mechanicalfactor during manufacture is suppressed. By preventing an electrolyticcapacitor having the PTC function from being mechanical damaged duringmanufacture, the electrolytic capacitor having the PTC function can bemanufactured stably and easily.

According to the electrolytic capacitor manufacturing method accordingto the second aspect of the invention, at the time of connecting asheet-shaped resistance control layer (high polymer, conductiveparticles) having the PTC function to the second electrode layer and theelectrode lead, the surface process for exposing the conductiveparticles is performed on at least one of the first and second faces ofthe resistance control layer. After that, the first face of theprocessed resistance control layer is connected to the second electrodelayer and the second face is connected to the electrode lead.Consequently, the contact resistance between the resistance controllayer and the second electrode layer or electrode lead is reduced, sothat the resistance characteristic of the electrolytic capacitor havingthe PTC function can be reduced as much as possible.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view showing an external configuration of anelectrolytic capacitor according to a first embodiment of the invention.

FIG. 2 is an enlarged cross section showing a sectional configuration ofthe electrolytic capacitor illustrated in FIG. 1.

FIG. 3 is a partially enlarged cross section showing a sectionalconfiguration of the electrolytic capacitor illustrated in FIG. 2.

FIG. 4 is a flowchart showing the flow of a manufacturing processrelated to a method of manufacturing the electrolytic capacitoraccording to the first embodiment of the invention.

FIG. 5 is a flowchart for explaining a modification of the method ofmanufacturing the electrolytic capacitor according to the firstembodiment of the invention.

FIG. 6 is a cross section showing a modification of the configuration ofthe electrolytic capacitor according to the first embodiment of theinvention.

FIG. 7 is a cross section showing a sectional configuration of anelectrolytic capacitor according to a second embodiment of theinvention.

FIG. 8 is a partially enlarged cross section showing a sectionalconfiguration of the electrolytic capacitor illustrated in FIG. 7.

FIG. 9 is a flowchart showing the flow of a manufacturing process of amethod of manufacturing the electrolytic capacitor according to thesecond embodiment of the invention.

FIG. 10 is a flowchart for explaining a modification of the method ofmanufacturing the electrolytic capacitor according to the secondembodiment of the invention.

FIG. 11 is a flowchart showing the flow of a manufacturing process of amethod of manufacturing an electrolytic capacitor according to a thirdembodiment of the invention.

FIG. 12 is an external view showing an external configuration of anelectrolytic capacitor according to a fourth embodiment of theinvention.

FIG. 13 is an enlarged cross section showing a sectional configurationof the electrolytic capacitor illustrated in FIG. 12.

FIG. 14 is a partially enlarged cross section showing a sectionalconfiguration of the electrolytic capacitor illustrated in FIG. 13.

FIG. 15 is a flowchart showing the flow of a manufacturing process of amethod of manufacturing an electrolytic capacitor according to thefourth embodiment of the invention.

FIG. 16 is a partially enlarged cross section showing a sectionalconfiguration of an electrolytic capacitor as a comparative example ofthe electrolytic capacitor according to the fourth embodiment of theinvention.

FIG. 17 is a flowchart for explaining a modification of the method ofmanufacturing the electrolytic capacitor according to the fourthembodiment of the invention.

FIG. 18 is a flowchart for explaining a modification of theconfiguration of the electrolytic capacitor according to the fourthembodiment of the invention.

FIG. 19 is a flowchart for explaining another modification of theconfiguration of the electrolytic capacitor according to the fourthembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

First, the configuration of an electrolytic capacitor according to afirst embodiment of the invention will be briefly described withreference to FIGS. 1 and 2. FIGS. 1 and 2 show the configuration of themain part (a capacitor element 10) of the electrolytic capacitor. FIG. 1shows an external configuration and FIG. 2 shows an enlarged sectionalconfiguration taken along line II—II of FIG. 1.

The electrolytic capacitor has a structure that an anode lead and acathode lead (which are not shown) are connected to the capacitorelement 10 shown in FIGS. 1 and 2 and the capacitor element 10 iscovered with a mold resin (not shown) so that both of the anode lead andthe cathode lead are partially exposed. An electric reaction occurs inthe capacitor element 10 as a main part of the electrolytic capacitor.For example, the capacitor element 10 includes, as shown in FIGS. 1 and2, an anode 11, a dielectric layer 12 disposed so as to partially coverthe periphery (of one end) of the anode 11, a solid electrolyte layer 13disposed so as to cover the dielectric layer 12, and a cathode 14disposed so as to cover the solid electrolyte layer 13. That is, thecapacitor element 10 has a stacked structure in which the anode 11,dielectric layer 12, solid electrolyte layer 13, and cathode 14 arestacked in this order.

The anode 11 is a first electrode layer having a rough surface structurewhich is subjected to surface enlarging process (or roughened), and ismade of a valve metal such as aluminum (Al), titanium (Ti), tantalum(Ta), or niobium (Nb). More concretely, the anode 11 is, for example,metal foil of aluminum, titanium, or the like or is a metal sinteredbody made of tantalum or niobium. The details of the rough surfacestructure of the anode 11 subjected to surface enlargement process willbe described later (refer to FIG. 3).

The dielectric layer 12 is an oxide film formed by anodizing the surfacelayer of the anode 11 made of the valve metal. The dielectric layer 12is made of, for example, aluminum oxide (Al₂O₃) when the anode 11 ismade of aluminum.

The solid electrolyte layer 13 contains, for example, the conductivehigh polymer and a dopant for controlling the conductivity of theconductive high polymer, that is, has a configuration that theconductive high polymer is doped with the dopant. The conductive highpolymer is selected from, for example, at least one of the groupconsisting of polyaniline, polypyrrole, polythiophene, polyfuran, andtheir derivatives. A concrete example is polyethylene dioxythiophene asa derivative of polythiophene. The dopant is selected from, for example,at least one of the group consisting of alkylbenzene sulfonic acid, saltof the same, alkylnaphthalene sulfonic acid, salt of the same, andphosphoric acid. A concrete example is paratoluene sulfonic acid iron orisopyropyl naphthalene sulfonic acid iron. The electrolytic capacitor inwhich the capacitor element 10 includes the solid electrolyte layer 13is a so-called solid electrolytic capacitor.

The cathode 14 is a second electrode layer disposed so as to face theanode 11 while sandwiching the dielectric layer 12 and the solidelectrolyte layer 13. The cathode 14 has the function of an inherentelectrode and also a function (so-called PTC function) that resistanceincreases as the temperature rises in a predetermined temperature range,more concretely, resistance increases exponentially. The resistance ofthe cathode 14 having the PTC function increases by about 1,000 times ormore in the temperature range from about 60° C. or higher and 150° C. orlower (as compared with resistance at room temperature).

Particularly, the cathode 14 has the stack structure in which, forexample, two or more layers are stacked, and at least one of the two ormore layers has the PTC function. Concretely, the cathode 14 has, forexample, as shown in FIG. 2, a main electrode layer 14B for assuringconductivity and a sub electrode layer 14A disposed between the mainelectrode layer 14B and the solid electrolyte layer 13 and electricallyjoining the main electrode layer 14B to the solid electrolyte layer 13.That is, the cathode 14 has a two-layer structure in which the mainelectrode layer 14B is stacked on the sub electrode layer 14A. In thecathode 14, for example, the sub electrode layer 14A does not have thePTC function and only the main electrode layer 14B has the PTC function.

The sub electrode layer 14A contains, for example, carbon. The subelectrode layer 14A has not only the function of electrically joiningthe main electrode layer 14B to the solid electrolyte layer 13 but also,for example, the function of preventing migration of a specificcomponent (for example, silver (Ag)) in the main electrode layer 14B inthe environments of high temperature and high moisture in the case wherethe main electrode layer 14B comes into direct contact with the solidelectrolyte layer 13.

The main electrode layer 14B contains, for example, a metal. Concretely,the main electrode layer 14B contains, for example, a high polymer as amain component and conductive particles as a sub component held in thehigh polymer. That is, the main electrode layer 14B is a so-calledpolymer PTC (P-PTC) layer. The high polymer is, for example, one of thegroup consisting of epoxy resin, poly vinylidene fluoride (PVDF), andpolyethylene (PE). The conductive particles are, for example, metalparticles of nickel (Ni), copper (Cu), aluminum (Al), tungsten (W),molybdenum (Mo), zinc (Zn), cobalt (Co), platinum (Pt), gold (Au),silver (Ag), and the like, or conductive ceramic particles of tungstencarbide (WC), titanium nitride (TiN), zirconium nitride (ZrN), titaniumcarbide (TiC), titanium boride (TiB₂), molybdenum silicide (MoSi₂), andtantalum boride (TaB₂).

For reference sake, the anode lead and the cathode lead are made of, forexample, a metal such as iron (Fe) or copper (Cu) or a plated metalobtained by performing a plating process (for example, tinning (Sn) orplating of tin lead (SnPb)) on the metals, and are connected to theanode 11 and the cathode 14, respectively, of the capacitor element 10.The mold resin is, for example, an insulating resin such as epoxy resin.

The detailed configuration of the capacitor element 10 will now bedescribed with reference to FIG. 3. FIG. 3 is a partially enlarged viewshowing a sectional configuration of the capacitor element 10illustrated in FIG. 2.

In the capacitor element 10, for example, as shown in FIG. 3, thedielectric layer 12, solid electrolyte layer 13, and cathode 14 (the subelectrode layer 14A and the main electrode layer 14B) are stacked inthis order so as to cover the anode 11. In the capacitor element 10, torealize larger capacity by increasing the surface area of the anode 11,the surface enlarging process (or roughening process) is performed onthe anode 11 as described above, so that the anode 11 has a fine surfacerough structure. The surface rough structure of the anode 11 isreflected and the dielectric layer 12 disposed so as to cover the anode11 also has a fine rough structure. Further, the solid electrolyte layer13 and the cathode 14 (sub electrode layer 14A and main electrode layer14B) are disposed so as to cover the dielectric layer 12 having the finerough structure. In particular, the dielectric layer 12 forms aplurality of pores 12H as parts of the rough structure, and the solidelectrolyte layer 13 is partially entered in the plurality of pores 12Hformed by the dielectric layer 12.

In the electrolytic capacitor shown in FIGS. 1 to 3, charges areaccumulated in the capacitor element 10 when current is passed to thecapacitor element 10 via the not-shown anode and cathode leads. In thiscase, by using the cathode 14 (main electrode layer 14B) having the PTCfunction, destruction of the electrolytic capacitor caused by heatgenerated at the time of short circuit is prevented. Specifically, forexample, when the overvotlage or backward voltage is applied to theelectrolytic capacitor, the dielectric layer 12 is partially broken andshort circuit occurs. Due to the short circuit, excess current flowsamong the anode 11, solid electrolyte layer 13, and cathode 14 (subelectrode layer 14A and main electrode layer 14B) and heat is generated.By the heat generation at the time of short circuit, the temperature ofthe main electrode layer 14B rises and resistance increasesexponentially. As a result, the excess current flowing in the capacitorelement 10 is suppressed, so that destruction of the capacitor element10 due to the excess current is suppressed. The factors of rise in thetemperature of the main electrode layer 14B include not only the heatgeneration at the time of short circuit but also Joule's heat caused byexcess current. As the temperature of the main electrode layer 14Bdecreases, the resistance of the main electrode layer 14B alsodecreases, so that the capacitor element 10 is reset to the state wherecurrent can be passed.

The principle that the main electrode layer 14B has the PTC function isas follows. At a stage before temperature rise, the conductive particlesconstruct a chain (what is called a conductive path) in the high polymerof the main electrode layer 14B. Since the chain is stably held by thehigh polymer, based on the existence of the chain, the main electrodelayer 14B is in a low resistance state. However, when the temperature ofthe main electrode layer 14B rises, due to the expansion phenomenon ofthe high polymer, the chain is disconnected, and the main electrodelayer 14B enters a high resistance state. Obviously, when thetemperature of the main electrode layer 14B decreases, the chain isre-constructed due to a contraction phenomenon of the high polymer, sothat the main electrode layer 14B enters again a low resistance state.Therefore, since the resistance state of the main electrode layer 14Bcan be reversibly changed by using the construction, disconnection, andre-construction mechanism of the chain, the main electrode layer 14B hasthe PTC function.

With reference to FIGS. 1 to 4, as a method of manufacturing theelectrolytic capacitor according to the embodiment of the invention, amethod of manufacturing the electrolytic capacitor having the capacitorelement 10 shown in FIGS. 1 to 3 will now be described. FIG. 4 is usedfor describing the flow of a manufacturing process of the method ofmanufacturing the electrolytic capacitor. As the materials of thecomponents of the electrolytic capacitor (capacitor element 10) havebeen already described above in detail, their description will not berepeated below.

At the time of manufacturing the electrolytic capacitor, first, thecapacitor element 10 shown in FIGS. 1 to 3 is formed. First, as theanode 11, for example, valve metal foil (such as aluminum foil ortitanium foil) subjected to the surface enlarging process, that is, theanode 11 having a fine surface roughness structure is prepared (stepS101 in FIG. 4). As the anode 11, for example, in place of the valvemetal foil subjected to the surface enlarging process, a valve metalsintered body of tantalum, niobium, or the like can be used. At the timeof preparing the anode 11, in place of using the valve metal foilsubjected to the surface enlarging process, the anode 11 may be formedby using unprocessed valve metal foil may be used and performing thesurface enlarging process on the valve metal foil by using chemicaletching or electric chemical etching.

Subsequently, by anodizing the surface layer of the anode 11, thedielectric layer 12 as an oxide film is formed so as to partially coverthe periphery of the anode 11 (step S102 in FIG. 4). As the dielectriclayer 12, for example, in the case of using aluminum foil as thematerial of the anode 11, the dielectric layer 12 can be formed by anoxide aluminum film. At the time of forming the dielectric layer 12, forexample, the anode 11 is impregnated in a formation solution and voltageis applied to the anode 12, thereby making anodic oxidation reactionprogressed. As the formation solution, for example, a buffer aqueoussolution containing ammonium borate, ammonium phosphate, organic acidammonium, or the like is used. Concretely, adipic acid ammonium aqueoussolution or the like is used. The voltage applied to the anode 11 can befreely set within the range from a few V to hundreds V in accordancewith the thickness of the dielectric layer 12.

Subsequently, by generating conductive high polymer doped with a dopantso as to cover the dielectric layer 12, the solid electrolyte layer 13is formed so as to include the conductive high polymer (step S103 inFIG. 4). At the time of forming the solid electrolyte layer 13, forexample, a solution (monomer solution) obtained by dispersing monomer,dopant, and oxidizer in a solvent is prepared. The monomer solution isapplied on the surface of the dielectric layer 12 and is heated toperform oxidation polymerization on the monomer by using the oxidizer inthe monomer solution, thereby generating conductive high polymer.Preferably, after the conductive high polymer is generated, for example,by washing the conductive high polymer with water, alcohol, acetone,hexane, or the like, the unpolymerized monomer included in theconductive high polymer, excessive dopant which has not been doped inthe conductive high polymer, used oxidizer, and the like are washed andremoved. The heating temperature and heating time of the monomersolution can be properly set in consideration of, for example,reactivity (polymerization) of the monomer, reactivity (rate ofoxidation) of the oxidizer, and the like.

At the time of preparing the monomer solution, as the monomer, forexample, at least one material selected from the group consisting ofaniline, pyrrole, tiophene, furan, thiophene vinylene,isothia-naphthene, acetylene, p-phenylene, phenylene vinylene, methoxyvinylne, methoxy phenylene, phenylene sulfide, phenylene oxide,anthracene, naphthalene, pyrene, azulene, selenophene, tellurophene, andtheir derivatives is used. Concretely, 3,4-ethylenedioxythiophene or thelike is used.

As a dopant, for example, both of donor dopant and acceptor dopant canbe used and at least one material selected from the group consisting ofthe following series of materials is used. Examples of the donor dopantsare alkali metals such as lithium (Li), sodium (Na), and potassium (K)and alkali-earth metals such as calcium (Ca). Examples of the acceptordopants are halogens such as chlorine (Cl₂), bromine (Br₂), and iodine(I₂), Lewis acids such as phosphorus fluoride (PF₃), arsenic fluoride(AsF₅), and boron fluoride (BF₃), proton acids such as hydrogen fluoride(HF), hydrogen chloride (HCl), nitric acid (HNO₃), sulfuric acid(H₂SO₄), phosphoric acid (H₃PO₄), and perchloric acid (HClO₄),alkylbenzene sulfonic acids (for example, para-toluenesulfonic acid) andalkylnaphthalenesulfonic acids and their salts (for example,para-toluenesulfonic acid sodium and alkylnaphthalenesulfonic acidsodium), transition-metal compounds such as ferric chloride (FeCl₃),iron perchloric acid (FeOCl₂), titanium chloride (TiCl₄), and tungstenchloride (WCl₃), and electrolyte anions such as chlorine ion (Cl⁻),bromine ions (Br⁻), iodine ion (I⁻), perchloric acid ion (ClO₄ ⁻),phosphorus fluoride ion (PF₃ ⁻), boron fluoride ion (BF₃ ⁻), and arsenicfluoride ion (AsF₃ ⁻).

As the oxidizer, for example, halogen such as iodine or bromine, a metalhalogen compound such as silicon pentafluoride (SiF₅), proton acid suchas sulfuric acid, oxygen compound such as sulfur trioxide (SO₃), sulfatesuch as cerium sulfate (Ce(SO₄)₂), persulate such as sodium persulfate(Na₂S₂O₈), peroxide such as hydrogen peroxide (H₂O₂), alkylbenzenesulfonate (for example, para-toluenesulfonic acid iron), or the like isused.

As the solvent, for example, water, organic solvent such as butanol isused.

The conductive high polymer generated by the above-described oxidationpolymerization reaction is, for example, at least one material selectedfrom the group consisting of polyaniline, polypyrrole, polythiophene,polyfuran, polythiophenevinylene, poly-isothia-naphthene, polyacetylene,poly-p-phenylene, polyphenylene vinylene, poly methoxy vinylne, polymethoxy phenylene, polyphenylene sulfide, poly phenylene oxide,polyanthracene, polynaphthalene, polypyrene, polyazulene,polyselenophene, polytellurophene, and their derivatives and,concretely, polyethylenedioxythiophene. An example of a desirableconductive high polymer is a conjugated-system high polymer having aone-dimensional chain in a high polymer skeleton and having the electrondonor function or electron acceptor function (so-called dopaminefunction).

Description of the process of manufacturing the electrolytic capacitorwill be continued. After formation of the stacked structure in which theanode 11, dielectric layer 12, and solid electrolyte layer 13 arestacked in this order, the cathode 14 having the PTC function is formedso as to cover the solid electrolyte layer 13 (step S104 in FIG. 4).

An example of the procedure of forming the cathode 14 is as follows.First, a carbon paste is applied on the surface of the solid electrolytelayer 13 and dried so as to form a film, thereby forming the subelectrode layer 14A (step S1041). Subsequently, as a metal paste forassuring the PTC function, a metal paste containing high polymer andconductive particles is prepared (step S1042). At the time of preparingthe metal paste, for example, at least one of the group consisting epoxyresin, polyvinylidene fluoride (PVDF), and polyethylene (PE) is used asthe high polymer, and metal particles of nickel (Ni), copper (Cu),aluminum (Al), tungsten (W), molybdenum (Mo), zinc (Zn), cobalt (Co),platinum (Pt), gold (Au), silver (Ag), and the like, or conductiveceramic particles of tungsten carbide (WC), titanium nitride (TiN),zirconium nitride (ZrN), titanium carbide (TiC), titanium boride (TiB₂),molybdenum silicide (MoSi₂), and tantalum boride (TaB₂) are used as theconductive particles. In the case of using metal particles as theconductive particles, it is preferable to use filament metal particles.Specifically, at the time of preparing the metal paste, for example,first, when the high polymer is liquid at room temperature, the liquidhigh polymer may be used as it is. Second, when the high polymer is notliquid at room temperature, the high polymer may be dissolved in asolvent so as to become liquid and the resultant liquid high polymer maybe used. Third, when the high polymer is very hard at room temperatureand there is no proper solvent in which the high polymer can bedissolved at room temperature, the high polymer may be heated todecrease its viscosity so as to enter an almost liquid state, and theresultant high polymer may be used. Finally, the metal paste is suppliedonto the surface of the sub electrode layer 14A and dried so as to forma film, thereby forming the main electrode layer 14B having the PTCfunction so as to have the configuration in which the conductiveparticles are held in the high polymer (step S1043). As the method ofsupplying the metal paste, for example, coating methods (such as spraymethod, roller method, and spin coating), impregnating methods(so-called dipping method), printing methods (such as screen printingand pad application), and the like can be used. In such a manner, thecathode 14 is formed so as to have the two-layer structure including thesub electrode layer 14A and the main electrode layer 14B. As a result,the capacitor element 10 having the stacked structure in which the anode11, dielectric layer 12, solid electrolyte layer 13, and cathode 14 (subelectrode layer 14A and main electrode layer 14B) are stacked in thisorder is completed.

After the capacitor element 10 is formed, an electrolytic capacitor isassembled by using the capacitor element 10. For example, an anode leadis connected to the anode 11 in the capacitor element 10, a cathode leadis connected to the cathode 14 (step S105 in FIG. 4), and the peripheryof the capacitor element 10 is covered with a mold resin so as topartially expose both of the anode and cathode leads (step S106 in FIG.4). By the operation, an electrolytic capacitor having the structure inwhich the anode and cathode leads are connected to the capacitor element10 and the periphery of the capacitor element 10 is covered with themold resin so that both of the anode and cathode leads are partiallyexposed is completed. At the time of connecting the anode and cathodeleads to the capacitor element 10, for example, they may be connecteddirectly by using welding or caulking or indirectly by using aconductive adhesive.

In the method of manufacturing the electrolytic capacitor according tothe embodiment, the cathode 14, concretely, the main electrode layer 14Bis formed so as to have the PTC function. On the basis of the principleof the PTC function, the PTC function is given to the main electrodelayer 14B in the cathode 14. In this case, different from theconventional electrolytic capacitor method in which a PTC thermistor isconnected to a capacitor element to give the PTC function to anelectrolytic capacitor so that the process of manufacturing theelectrolytic capacitor is more complicated and the number ofmanufacturing processes increases by the amount corresponding to the PTCthermistor connecting process, the process of connecting the PTCthermistor to the capacitor element 10 is unnecessary. Consequently,complication of the electrolytic capacitor manufacturing process andincrease in the number of manufacturing processes caused by the PTCthermistor connecting process is prevented. Moreover, to form the mainelectrode layer 14B having the PTC function, it is sufficient to use, asthe material of the main electrode layer 14B, the materials (highpolymer and conductive particles) capable of assuring the PTC functionin place of a material which cannot assure the PTC function. That is,since the electrolytic capacitor can be manufactured by using theexisting method of manufacturing an electrolytic capacitor which doesnot have the PTC function only with the change point of forming the mainelectrode layer 14B by using the material for assuring the PTC function,the electrolytic capacitor manufacturing process is not complicated.Therefore, since the electrolytic capacitor can be manufactured easilywhile preventing destruction of the electrolytic capacitor caused byheat generated at the time of short circuit by using the PTC function,the electrolytic capacitor having the PTC function can be manufacturedas easy as possible. As a result, high productivity can be assured byincreasing the manufacture yield of the electrolytic capacitor havingthe PTC function.

In the electrolytic capacitor according to the embodiment, the cathode14, concretely, the main electrode layer 14B as part of the cathode 14has the PTC function. Consequently, different from the conventionalelectrolytic capacitor in which a PTC thermistor is externally attachedas a component other than the capacitor element to the capacitorelement, the cathode 14 as the inherent component of the capacitorelement 10 has the PTC function. In this case, different from theconventional case, the PTC function is assured without increasing thenumber of components of the electrolytic capacitor, so that theconfiguration of the electrolytic capacitor is prevented from becomingcomplicated to assure the PTC function. Therefore, the PTC function canbe assured with the simplest configuration.

In the embodiment, the main electrode layer 14B having the PTC functionis formed by supplying the material (high polymer and conductiveparticles) for assuring the PTC function onto the surface of the subelectrode layer 14A so as to form a film. However, the invention is notalways limited to the embodiment. For example, as shown in FIG. 5, inplace of the method of forming the main electrode layer 14B on the subelectrode layer 14A, the main electrode layer 14B separately formed maybe connected to the sub electrode layer 14A. FIG. 5 is to describe amodification of the electrolytic capacitor manufacturing method andshows the flow of a manufacturing process corresponding to FIG. 4. Inthe electrolytic capacitor manufacturing method, as shown in FIGS. 1 to3 and FIG. 5, the anode 11 is prepared (step S201), the dielectric layer12 and the solid electrolyte layer 13 are formed on the anode 11 (stepsS202 and S203) and, on the solid electrolyte layer 13, the cathode 14 isformed so as to include the main electrode layer 14B separately formed(step S204). Concretely, the sub electrode layer 14A is formed on thesolid electrolyte layer 13 (step S2041). After that, by applying thematerial (high polymer and conductive particles) for assuring the PTCfunction in a sheet shape, a conductive high polymer sheet is formed(step S2042). By connecting the conductive high polymer sheet as themain electrode layer 14B to the surface of the sub electrode layer 14A(step S2043), the cathode 14 is formed so as to have the two-layerstructure including the sub electrode layer 14A and the main electrodelayer 14B. At the time of connecting the conductive high polymer sheetto the sub electrode layer 14A, for example, to assure attachability ofthe main electrode layer 14B to the sub electrode layer 14A, it ispreferable to use thermo compression bonding process as the connectingprocess. In such a manner, the capacitor element 10 having the stackedstructure in which the anode 11, dielectric layer 12, solid electrolytelayer 13, and cathode 14 (sub electrode layer 14A and main electrodelayer 14B) are stacked in this order is formed. After that, byconnecting the anode lead and the cathode lead to the anode 11 and thecathode 14 in the capacitor element 10, respectively (step S205) andcovering the periphery of the capacitor element 10 so that both of theanode and cathode leads are partially exposed (step S206), theelectrolytic capacitor is completed. In this case as well, the PTCfunction is given to the main electrode layer 14B in the cathode 14, sothat effects similar to those of the foregoing embodiment can beobtained. The procedure other than the above-described procedure relatedto the electrolytic capacitor manufacturing method shown in FIG. 5 issimilar to, for example, that of the case shown in FIG. 4.

Although the only the main electrode layer 14B in the cathode 14 has thePTC function in the embodiment, the invention is not limited to theembodiment but, for example, in place of the main electrode layer 14B,only the sub electrode layer 14A may have the PTC function or both ofthe sub electrode layer 14A and the main electrode layer 14B may havethe PTC function. In the case where only the sub electrode layer 14A hasthe PTC function in place of the main electrode layer 14B, for example,a carbon paste containing high polymer and conductive particles is usedas the material of the sub electrode layer 14A (material for assuringthe PTC function) and the sub electrode layer 14A is formed by a processsimilar to that in the case of forming the main electrode layer 14B inthe foregoing embodiment, thereby enabling the PTC function to be givento the sub electrode layer 14A. In this case, for example, high polymersimilar to that in the foregoing embodiment is used as the high polymer,carbon particles such as carbon black (CB) particles are used as theconductive particles, and a general metal paste (such as silver paste)is used as the material of the main electrode layer 14 (the materialwhich does not assure the PTC function). In the case of giving the PTCfunction to both of the sub electrode layer 14A and the main electrodelayer 14B, for example, it is sufficient to combine the sub electrodelayer 14A having the PTC function and the main electrode layer 14Bhaving the PTC function. Also in those cases, the PTC function is givento the cathode 14, so that effects similar to those of the foregoingembodiment can be obtained.

Although the cathode 14 has the two-layer structure (the sub electrodelayer 14A and the main electrode layer 14B) in the embodiment, theinvention is not always limited to the embodiment. The number of stackedlayers of the cathode 14 can be freely changed to the number of 2 orlarger. In this case as well, as long as the cathode 14 has a resistancecharacteristic enough to function as an electrode and can assure the PTCfunction, effects similar to those of the foregoing embodiment can beobtained. Obviously, in this case as well, for example, only a layer aspart of the stacked structure of the cathode 14 may have the PTCfunction or all of the layers in the stacked structure may have the PTCfunction.

Although the cathode 14 having the PTC function has the stackedstructure (sub electrode layer 14A and main electrode layer 14B) in theembodiment, the invention is not always limited to the embodiment. Forexample, as shown in FIG. 6, the cathode 14 may have a single-layerstructure. In this case, the cathode 14 may have a configurationcorresponding to that of the main electrode layer 14B having the PTCfunction described in the foregoing embodiment or that of the subelectrode layer 14A having the PTC function in the modification.However, when the resistance characteristic of the conductive particles(such as carbon particles) contained in the sub electrode layer 14Ahaving the PTC function and that of the conductive particles (such asmetal particles or conductive ceramic particles) contained in the mainelectrode layer 14B having the PTC function are compared with eachother, the resistance value based on conductive particles in the metalparticles or conductive ceramic particles is lower than that in thecarbon particles. Consequently, considering that the cathode 14 has notonly the PTC function but also the electrode function, it is preferablethat the cathode 14 has the configuration corresponding to that of themain electrode layer 14B having the PTC function. In this case as well,effects similar to those of the foregoing embodiment can be obtained.The configuration characteristics other than the above of the capacitorelement 10 shown in FIG. 6 are similar to, for example, those of FIG. 2.

Second Embodiment

A second embodiment of the invention will now be described.

FIG. 7 shows a sectional configuration of the capacitor element 10described in the first embodiment as the configuration of anelectrolytic capacitor according to the second embodiment. The sectionalconfiguration corresponds to FIG. 2. The electrolytic capacitoraccording to the second embodiment has a configuration (refer to FIG. 1)similar to that of the electrolytic capacitor of the first embodimentexcept for the point that a cathode 114 having a three-layer structure(a sub electrode layer 114A, a main electrode layer 114B, and anauxiliary electrode layer 114C) is provided in place of the cathode 14having the two-layer structure (the sub electrode layer 14A and the mainelectrode layer 14B).

The cathode 114 in the electrolytic capacitor of the second embodimenthas the PTC function and contains at least one of the metal particlesand conductive ceramic particles as the conductive particles. Inparticular, the cathode 114 has, for example, a stacked structure inwhich two or more layers are stacked, and at least one of the two ormore layers contains the conductive particles and has the PTC function.Concretely, for example, as shown in FIG. 7, the cathode 114 has themain electrode layer 114B for assuring conductivity, the sub electrodelayer 114A disposed between the main electrode layer 114B and the solidelectrolyte layer 13, for electrically joining the main electrode layer114B to the solid electrolyte layer 13, and the auxiliary electrodelayer 114C which is disposed on the side opposite to the sub electrodelayer 114A while sandwiching the main electrode layer 114B, containsconductive particles, and has the PTC function. Specifically, thecathode 114 has, for example, a three-layer structure in which the subelectrode layer 114A, main electrode layer 114B, and auxiliary electrodelayer 114C are stacked in this order. In the cathode 114, for example,as described above, the sub electrode layer 114A and the main electrodelayer 114B do not have the PTC function but only the auxiliary electrodelayer 114C has the PTC function.

The sub electrode layer 114A is constructed by containing, for example,carbon. The sub electrode layer 114A has, for example, not only thefunction of electrically joining the main electrode layer 114B to thesolid electrolyte layer 13 but also the function of, for example, in thecase where the main electrode layer 114B is in direct contact with thesolid electrolyte layer 13, preventing migration of a specific component(for example, silver (Ag)) in the main electrode layer 114B in theenvironments of high temperature and high moisture.

The main electrode layer 114B contains, for example, a metal which isconcretely silver (Ag).

The auxiliary electrode layer 114C is formed by applying a material forassuring the PTC function on the surface of an under layer (in thiscase, the main electrode layer 114B), concretely, a liquid high polymercontaining conductive particles as the material (metal paste) forassuring the PTC function. The auxiliary electrode layer 114C contains,for example, a film-shaped high polymer as a main component formed byusing the liquid high polymer, and conductive particles as a subcomponent held in the film-shaped high polymer. That is, the auxiliaryelectrode layer 114C is a so-called polymer PTC (P-PTC) layer. Theliquid high polymer contains at least one of a thermosetting highpolymer and a soluble thermoplastic high polymer (a thermoplastic highpolymer which does not directly become a liquid state at roomtemperature but indirectly becomes a liquid state due to the existenceof a solvent which can be dissolved at room temperature) except for aninsoluble thermoplastic high polymer (a thermoplastic high polymer whichdoes not directly become a liquid state at room temperature and,moreover, does not also indirectly become a liquid state since nosolvent which can be dissolved at room temperature exists). An exampleof the thermosetting high polymer is an epoxy resin and an example ofthe soluble thermoplastic high polymer is polyvinylidene fluoride(PVDF). The conductive particles are, for example, metal particles ofnickel (Ni), copper (Cu), aluminum (Al), tungsten (W), molybdenum (Mo),zinc (Zn), cobalt (Co), platinum (Pt), gold (Au), silver (Ag), and thelike, or conductive ceramic particles of tungsten carbide (WC), titaniumnitride (TiN), zirconium nitride (ZrN), titanium carbide (TiC), titaniumboride (TiB₂), molybdenum silicide (MoSi₂), and tantalum boride (TaB₂).

An example of the sectional configuration of the capacitor element 10having the cathode 114 (sub electrode layer 114A, main electrode layer114B, and auxiliary electrode layer 114C) is as shown in FIG. 8.

With reference to FIG. 1 and FIGS. 7 to 9, as a method of manufacturingthe electrolytic capacitor according to the second embodiment, a methodof manufacturing the electrolytic capacitor having the capacitor element10 shown in FIGS. 1, 7, and 8 will now be described. FIG. 9 is used fordescribing the flow of a manufacturing process of the method ofmanufacturing the electrolytic capacitor. As the materials of thecomponents of the electrolytic capacitor (capacitor element 10) havebeen already described above in detail, their description will not berepeated below.

The electrolytic capacitor manufacturing method of the second embodimentis similar to that of the first embodiment (refer to FIG. 4) except forthe point that the electrolytic capacitor is manufactured so as toinclude the cathode 114 having the three-layer structure (sub electrodelayer 114A, main electrode layer 114B, and auxiliary electrode layer114C). At the time of manufacturing the electrolytic capacitor, first,the capacitor element 10 shown in FIGS. 1, 7, and 8 is formed. First, asthe anode 11, for example, valve metal foil subjected to the surfaceenlarging process is prepared (step S301 in FIG. 9), after that, thedielectric layer 12 is formed so as to partially cover the periphery ofthe anode 11 (step S302 in FIG. 9), and the solid electrolyte layer 13is formed so as to cover the dielectric layer 12 (step S303 in FIG. 9).

Subsequently, the cathode 114 having the PTC function is formed so as tocover the solid electrolyte layer 13 (step S304 in FIG. 9).

An example of the procedure of forming the cathode 114 is as follows.First, a carbon paste is applied on the surface of the solid electrolytelayer 13 and dried so as to form a film, thereby forming the subelectrode layer 114A (step S3041). Subsequently, a metal paste is formedon the surface of the sub electrode layer 114A and dried to form a film,thereby forming the main electrode layer 114B (step S3042). At the timeof forming the main electrode layer 114B, for example, a silver (Ag)paste is used as the metal paste. Subsequently, as the material forassuring the PTC function, the metal paste containing the liquid highpolymer and conductive particles is prepared (step S3043). At the timeof preparing the metal paste, for example, at least one of thethermosetting high polymer such as epoxy resin and the solublethermoplastic high polymer such as polyvinylidene fluoride (PVDF) isused as the liquid high polymer, and at least one of the metal particlesor conductive ceramic particles are used as the conductive particles.Concretely, metal particles of nickel (Ni), copper (Cu), aluminum (Al),tungsten (W), molybdenum (Mo), zinc (Zn), cobalt (Co), platinum (Pt),gold (Au), silver (Ag), and the like, or conductive ceramic particles oftungsten carbide (WC), titanium nitride (TiN), zirconium nitride (ZrN),titanium carbide (TiC), titanium boride (TiB₂), molybdenum silicide(MoSi₂), and tantalum boride (TaB₂) are used as the conductiveparticles. In the case of using metal particles as the conductiveparticles, it is preferable to use filament metal particles. Finally, ametal paste is supplied onto the surface of the main electrode layer114B and dried to form a film, thereby forming the auxiliary electrodelayer 114C having the PTC function so as to contain the film-shaped highpolymer formed from the liquid high polymer and the conductive particlesheld in the film-shaped high polymer (step S3044). As the method ofsupplying the metal paste, for example, coating methods (such as spraymethod, roller method, and spin coating), impregnating methods(so-called dipping method), printing methods (such as screen printingand pad application), and the like can be used. In such a manner, thecathode 114 is formed so as to have the three-layer structure includingthe sub electrode layer 114A, the main electrode layer 114B, andauxiliary electrode layer 114C. As a result, the capacitor element 10having the stacked structure in which the anode 11, dielectric layer 12,solid electrolyte layer 13, and cathode 114 (sub electrode layer 114A,main electrode layer 114B, and auxiliary electrode layer 114C) arestacked in this order is completed.

Finally, for example, an anode lead is connected to the anode 11 in thecapacitor element 10, a cathode lead is connected to the cathode 114(step S305 in FIG. 9), and the periphery of the capacitor element 10 iscovered with a mold resin so as to partially expose both of the anodeand cathode leads (step S306 in FIG. 9). By the operation, anelectrolytic capacitor having the structure in which the anode andcathode leads are connected to the capacitor element 10 and theperiphery of the capacitor element 10 is covered with the mold resin sothat both of the anode and cathode leads are partially exposed iscompleted.

In the method of manufacturing the electrolytic capacitor according tothe embodiment, the cathode 114, concretely, the auxiliary electrodelayer 114C is formed so as to have the PTC function. On the basis of theprinciple of the PTC function, the PTC function is given to theauxiliary electrode layer 114C in the cathode 114. In this case, byforming the auxiliary electrode layer 114C so as to contain at least oneof the metal particles or conductive ceramic particles as conductiveparticles, based on the low resistance characteristic of the metalparticles or conductive ceramic particles, the low resistancecharacteristic of the electrolytic capacitor is achieved. Consequently,while preventing destruction of the electrolytic capacitor caused byheat generated at the time of short circuit by using the PTC function,the low resistance characteristic of the electrolytic capacitor can beachieved. Therefore, the resistance characteristic of the electrolyticcapacitor having the PTC function can be decreased as much as possible.

Particularly, in the embodiment, the auxiliary electrode layer 114C(film-shaped high polymer and conductive particles) having the PTCfunction is formed by supplying the metal past (liquid high polymer andconductive particles) onto the surface of the main electrode layer 114B.As compared with, for example, the case of preliminarily forming anauxiliary electrode layer in a sheet shape (conductive high polymersheet) and joining the sheet-shaped auxiliary electrode layer to thesurface of the main electrode layer 114B (by bonding or thermocompression bonding), the resistance characteristic of the electrolyticcapacitor decreases only by the amount corresponding to the contactresistance in the bonded part. Therefore, also from this viewpoint, theinvention can contribute to decrease in the resistance of theelectrolytic capacitor.

In addition, in the electrolytic capacitor according to the embodiment,the resistance characteristic decreases while assuring the PTC function.Thus, the PTC function can be assured with resistance as low aspossible.

In the embodiment, the auxiliary electrode layer 114C is formed bysupplying the material (liquid high polymer and conductive particles)for assuring the PTC function onto the surface of the main electrodelayer 114B so as to form a film. However, the invention is not alwayslimited to the embodiment. For example, as shown in FIG. 10, in place ofthe method of forming the auxiliary electrode layer 114C on the surfaceof the main electrode layer 114B, the auxiliary electrode layer 114Cseparately formed may be connected to the surface of the main electrodelayer 114B. FIG. 10 is to describe a modification of the electrolyticcapacitor manufacturing method and shows the flow of a manufacturingprocess corresponding to FIG. 9. In the electrolytic capacitormanufacturing method, as shown in FIGS. 1, 7, 8, and 10, the anode 11 isprepared (step S401), the dielectric layer 12 and the solid electrolytelayer 13 are formed on the anode 11 (steps S402 and S403) and, on thesolid electrolyte layer 13, the cathode 114 is formed so as to includethe sub electrode layer 114A, the main electrode layer 114B, and theauxiliary electrode layer 114C separately formed (step S404).Concretely, the sub electrode layer 114A is formed on the solidelectrolyte layer 13 (step S4041), the main electrode layer 114B isformed on the sub electrode layer 114A (step S4042) and, after that, byforming a sheet by using the material (liquid high polymer andconductive particles) for assuring the PTC function, a conductive highpolymer sheet is formed (step S4043). By connecting the conductive highpolymer sheet as the auxiliary electrode layer 114C to the surface ofthe main electrode layer 114B (step S4044), the cathode 114 is formed soas to have the three-layer structure including the sub electrode layer114A, the main electrode layer 114B, and the auxiliary electrode layer114C. As the process of bonding the conductive high polymer sheet to themain electrode layer 114B, for example, a bonding process or a thermocompression bonding can be used. In such a manner, the capacitor element10 having the stacked structure in which the anode 11, dielectric layer12, solid electrolyte layer 13, and cathode 14 (sub electrode layer114A, main electrode layer 114B, and auxiliary electrode layer 114C) arestacked in this order is formed. After that, by connecting the anodelead and the cathode lead to the anode 11 and the cathode 114 in thecapacitor element 10, respectively (step S405) and covering theperiphery of the capacitor element 10 so that both of the anode andcathode leads are partially exposed (step S406), the electrolyticcapacitor is completed. In this case as well, the PTC function is givento the auxiliary electrode layer 114C in the cathode 114, so thateffects similar to those of the foregoing embodiment can be obtained.However, it should be noted that, as described above, when the auxiliaryelectrode layer 114C is bonded to the main electrode layer 114B, ascompared with the case of forming the film of the auxiliary electrodelayer 114C on the surface of the main electrode layer 114B, theresistance characteristic of the electrolytic capacitor rises only bythe amount corresponding to the contact resistance between the mainelectrode layer 114B and the auxiliary electrode layer 114C. Theprocedure other than the above-described procedure related to theelectrolytic capacitor manufacturing method shown in FIG. 10 is similarto, for example, that of the case shown in FIG. 9.

Although the only the auxiliary electrode layer 114C in the cathode 114(the sub electrode layer 114A, main electrode layer 114B, and auxiliaryelectrode layer 114C) has the PTC function in the embodiment, theinvention is not limited to the embodiment but, for example, in place ofthe auxiliary electrode layer 114C, only the sub electrode layer 114A ormain electrode layer 114B may have the PTC function or a combination ofarbitrary two layers out of the sub electrode layer 114A, the mainelectrode layer 114B, and the auxiliary electrode layer 114C may havethe PTC function. Alternately, all of the sub electrode layer 114A, themain electrode layer 114B, and the auxiliary electrode layer 114C mayhave the PTC function. In the case of giving the PTC function only tothe sub electrode layer 114A, for example, a carbon paste containingconductive particles is used as the material of the sub electrode layer114A (material for assuring the PTC function) and the sub electrodelayer 114A is formed by a process similar to that in the case of formingthe auxiliary electrode layer 114C in the foregoing embodiment, therebyenabling the PTC function to be given to the sub electrode layer 114A.In this case, for example, at least one of the metal particles andconductive particles described in the foregoing embodiment is used asthe conductive particles, and a general metal paste (such as silverpaste) is used as the material of the main electrode layer 114B and theauxiliary electrode layer 114C (the material which does not assure thePTC function). In the case of giving the PTC function only to the mainelectrode layer 114B, for example, the PTC function can be given to themain electrode layer 114B by forming the main electrode layer 114B by aprocess similar to that in the case of forming the auxiliary electrodelayer 114C in the foregoing embodiment. In this case, as the material ofthe auxiliary electrode layer 114C (the material which does not assurethe PTC function), for example, a general metal paste (such as silverpaste) is used. In the case of giving the PTC function to all of the subelectrode layer 114A, the main electrode layer 114B, and the auxiliaryelectrode layer 114C, for example, it is sufficient to combine the subelectrode layer 114A having the PTC function, the main electrode layer114B having the PTC function, and the auxiliary electrode layer 114Chaving the PTC function. Also in those cases, the PTC function is givento the cathode 114, so that effects similar to those of the foregoingembodiment can be obtained.

Although the cathode 114 has the three-layer structure (the subelectrode layer 114A, the main electrode layer 114B, and the auxiliaryelectrode layer 114C) in the embodiment, the invention is not alwayslimited to the embodiment. The number of stacked layers of the cathode114 can be freely changed to the number of 2 or larger. In this case aswell, as long as the cathode 114 has a resistance characteristic enoughto function as an electrode and can assure the PTC function, effectssimilar to those of the foregoing embodiment can be obtained. Obviously,in this case as well, for example, only a layer as part of the stackedstructure of the cathode 114 may have the PTC function or all of thelayers in the stacked structure may have the PTC function.

Although the cathode 114 having the PTC function has the stackedstructure (sub electrode layer 114A, main electrode layer 114B,auxiliary electrode layer 114C) in the embodiment, the invention is notalways limited to the embodiment. For example, the cathode 114 may havea single-layer structure. In this case, the cathode 114 may have aconfiguration corresponding to that of the auxiliary electrode layer114C having the PTC function described in the foregoing embodiment. Inthis case as well, effects similar to those of the foregoing embodimentcan be obtained.

The other configuration, operation, action, effect, and modification ofthe electrolytic capacitor according to the second embodiment and theother procedure, action, effect, and modification of the electrolyticcapacitor manufacturing method of the second embodiment are similar tothose of the first embodiment.

Third Embodiment

A third embodiment of the invention will now be described.

FIG. 11 is used to describe the flow of a manufacturing process of anelectrolytic capacitor manufacturing method of the third embodiment. Anelectrolytic capacitor manufactured by the electrolytic capacitormanufacturing method according to the third embodiment has aconfiguration (refer to FIGS. 1 to 3) similar to that of theelectrolytic capacitor of the first embodiment except for the point thatthe cathode 14 is formed by forming a film from a liquid material forassuring the PTC function. In the following, the configuration of theelectrolytic capacitor according to the third embodiment will bedescribed first with reference to FIGS. 1 to 3 and, after that, theelectrolytic capacitor manufacturing method of the third embodiment willbe described with reference to FIGS. 1 to 3 and FIG. 11. Since thematerials of the components of the electrolytic capacitor (capacitorelement 10) have been described in detail above, the description willnot be repeated.

The cathode 14 in the electrolytic capacitor of the third embodiment isformed by applying a liquid material onto the surface of the solidelectrolyte layer 13 has the PTC function. The “liquid material”directly becomes a liquid state (fluid state) without using a solvent atroom temperature (which is atmosphere temperature in normal environmentwhere the electrolytic capacitor manufacturing process is generallyperformed except for high-temperature environment intentionally set, andis concretely atmosphere temperature in a range from about 15° C. to 30°C.) or indirectly becomes the liquid state by being dissolved to thesolvent. The liquid material has a characteristic capable of directlyforming a film when supplied onto the surface of the solid electrolytelayer 13 by using a method such as coating, dipping, or printing. The“liquid state (fluid state)” denotes a concept including a paste stateas long as the material can be supplied onto the surface of the solidelectrolyte layer 13 and is a state where the material has viscosity ina range from about 100 cP to 1,000,000 cP.

In particular, the cathode 14 has, for example, as shown in FIG. 2, atwo-layer structure in which the main electrode layer 14B is stacked onthe sub electrode layer 14A. The main electrode layer 14B in the cathode14 contains, for example, a metal and is, concretely, formed as a filmby applying a liquid material (metal paste) on the surface of the subelectrode layer 14A. More concretely, the main electrode layer 14B isformed by using, as the liquid material for assuring the PTC function,the liquid high polymer containing the conductive particles and is apolymer PTC (P-PTC) layer constructed by containing a film-shaped highpolymer formed by using the liquid high polymer, and conductiveparticles held in the film-shaped high polymer. The liquid high polymeris a high polymer having the characteristic similar to that of theabove-described “liquid material” and, concretely, contains at least oneof a thermosetting high polymer and a soluble thermoplastic high polymer(a thermoplastic high polymer which does not directly become a liquidstate at room temperature but indirectly becomes a liquid state due tothe existence of a solvent which can be dissolved at room temperature)except for an insoluble thermoplastic high polymer (a thermoplastic highpolymer which does not directly become a liquid state at roomtemperature and, moreover, does not also indirectly become a liquidstate since no solvent which can be dissolved at room temperatureexists). An example of the thermosetting high polymer is an epoxy resinand an example of the soluble thermoplastic high polymer ispolyvinylidene fluoride (PVDF). The conductive particles are, forexample, metal particles of nickel (Ni), copper (Cu), aluminum (Al),tungsten (W), molybdenum (Mo), zinc (Zn), cobalt (Co), platinum (Pt),gold (Au), silver (Ag), and the like, or conductive ceramic particles oftungsten carbide (WC), titanium nitride (TiN), zirconium nitride (ZrN),titanium carbide (TiC), titanium boride (TiB₂), molybdenum silicide(MoSi₂), and tantalum boride (TaB₂).

The procedure of the electrolytic capacitor manufacturing method of thethird embodiment is similar to that of the electrolytic capacitormanufacturing method of the first embodiment (refer to FIG. 4) exceptfor the point that the cathode 14 is formed by forming a film by usingthe liquid material for assuring the PTC function. At the time ofmanufacturing the electrolytic capacitor, first, the capacitor element10 shown in FIGS. 1 to 3 is formed. First, as the anode 11, for example,valve metal foil subjected to the surface enlarging process is prepared(step S501 in FIG. 11), after that, the dielectric layer 12 is formed soas to partially cover the periphery of the anode 11 (step S502 in FIG.11), and the solid electrolyte layer 13 is formed so as to cover thedielectric layer 12 (step S503 in FIG. 11).

Subsequently, the cathode 14 having the PTC function is formed so as tocover the solid electrolyte layer 13 (step S504 in FIG. 11). The cathode14 is formed so as to have the PTC function by applying the liquidmaterial onto the surface of the solid electrolyte layer 13 so as toform a film.

An example of the procedure of forming the cathode 14 is as follows.First, a carbon paste as the liquid material is supplied onto thesurface of the solid electrolyte layer 13 and dried to form a film,thereby forming the sub electrode layer 14A (step S5041). As the methodof supplying the carbon paste, for example, coating methods (such asspray method, roller method, and spin coating), impregnating methods(so-called dipping method), printing methods, and the like can be used.Subsequently, by dispersing the conductive particles in the liquid highpolymer, a metal paste as the liquid material for assuring the PTCfunction is prepared (step S5042). At the time of preparing the metalpaste, for example, at least one of the thermosetting high polymer suchas epoxy resin and the soluble thermoplastic high polymer such aspolyvinylidene fluoride (PVDF) is used as the liquid high polymer, andat least one of the metal particles and conductive ceramic particles areused as the conductive particles. Concretely, examples of the metalparticles are nickel (Ni), copper (Cu), aluminum (Al), tungsten (W),molybdenum (Mo), zinc (Zn), cobalt (Co), platinum (Pt), gold (Au),silver (Ag), and the like, and examples of the conductive ceramicparticles are tungsten carbide (WC), titanium nitride (TiN), zirconiumnitride (ZrN), titanium carbide (TiC), titanium boride (TiB₂),molybdenum silicide (MoSi₂), and tantalum boride (TaB₂). In the case ofusing metal particles as the conductive particles, it is preferable touse filament metal particles. Finally, a metal paste is supplied ontothe surface of the sub electrode layer 14A so as to form a film, therebyforming the main electrode layer 14B having the PTC function so as tocontain the film-shaped high polymer formed from the liquid high polymerand the conductive particles held in the film-shaped high polymer (stepS5043). The method of supplying the metal paste is, for example, similarto that of the carbon paste in the case of forming the sub electrodelayer 14A. In such a manner, the cathode 14 is formed so as to have thetwo-layer structure including the sub electrode layer 14A and the mainelectrode layer 14B. As a result, the capacitor element 10 having thestacked structure in which the anode 11, dielectric layer 12, solidelectrolyte layer 13, and cathode 14 (sub electrode layer 14A and mainelectrode layer 14B) are stacked in this order is completed.

Finally, for example, an anode lead is connected to the anode 11 in thecapacitor element 10, a cathode lead is connected to the cathode 14(step S505 in FIG. 11), and the periphery of the capacitor element 10 iscovered with a mold resin so as to partially expose both of the anodeand cathode leads (step S506 in FIG. 11). By the operation, anelectrolytic capacitor having the structure in which the anode andcathode leads are connected to the capacitor element 10 and theperiphery of the capacitor element 10 is covered with the mold resin sothat both of the anode and cathode leads are partially exposed iscompleted.

In the method of manufacturing the electrolytic capacitor according tothe embodiment, at the time of forming the cathode 14 of the two-layerstructure (sub electrode layer 14A and main electrode layer 14B) havingthe PTC function on the solid electrolyte layer 13, a carbon paste issupplied onto the surface of the solid electrolyte layer 13 to form afilm, thereby forming the sub electrode layer 14A. By supplying a metalpaste (liquid high polymer and conductive particles) onto the surface ofthe sub electrode layer 14A, the main electrode layer 14B (film-statehigh polymer and conductive particles) is formed. On the basis of theprinciple of the PTC function, the PTC function is given to the mainelectrode layer 14B in the cathode 14. In the conventional electrolyticcapacitor manufacturing method, a PTC thermistor is bonded to thecapacitor element by thermo compression bonding to give the PTC functionto the electrolytic capacitor. Due to mechanical factors (excessiveexternal force applied to the capacitor element) at the time of thermocompression bonding, the dielectric layer tends to be damaged severelyduring manufacture. In the electrolytic capacitor manufacturing methodof the embodiment, different from the conventional electrolyticcapacitor manufacturing method, excessive external force is not appliedon the dielectric layer 12. Consequently, the dielectric layer 12 is noteasily damaged due to the mechanical factors during manufacture. Thus,high productivity can be assured by increasing the manufacture yield ofthe electrolytic capacitor while preventing destruction of theelectrolytic capacitor caused by heat generated at the time of shortcircuit by using the PTC function. Therefore, by preventing theelectrolytic capacitor having the PTC function from being destroyedmechanically during manufacture, the electrolytic capacitor having thePTC function can be stably manufactured.

The difference between the electrolytic capacitor manufacturing methodof the embodiment and the conventional electrolytic capacitormanufacturing method will be described for confirmation. In theembodiment, at the time of forming the main electrode layer 14B, a metalpaste is supplied onto the surface of the sub electrode layer 14A. Inthis case, external force is not completely prevented from being appliedto the dielectric layer 12 but external force based on the metal pastesupplying process is applied. However, obviously, the external forcebased on the metal paste supplying process is much smaller than thatbased on the compression bonding process and does not mechanicallydestroy the dielectric layer 12 during manufacture of the electrolyticcapacitor. Therefore, the possibility that the dielectric layer 12 isdestroyed due to external force based on the metal paste supplyingprocess is much smaller than the possibility that the dielectric layeris destroyed due to external force based on the compression bondingprocess.

Particularly, in the embodiment, the cathode 14, concretely, the mainelectrode layer 14B as part of the cathode 14 has the PTC function.Consequently, different from the conventional electrolytic capacitormanufacturing method in which a PTC thermistor is externally attached asa component other than the capacitor element to the capacitor element,the PTC function is given to the cathode 14 as the inherent component ofthe capacitor element 10. In this case, different from the conventionalcase, the PTC function is assured without increasing the number ofcomponents of the electrolytic capacitor, so that the configuration ofthe electrolytic capacitor is prevented from becoming complicated and itis unnecessary to externally attach a new component to the capacitorelement 10. Consequently, the number of manufacturing processes of theelectrolytic capacitor can be prevented from being increased. Therefore,since the electrolytic capacitor can be manufactured by using theexisting method of manufacturing the electrolytic capacitor having noPTC function only with the change point that the main electrode layer14B is formed by using the liquid material (liquid high polymer andconductive particles) for assuring the PTC function, the electrolyticcapacitor having the PTC function can be manufactured as simple aspossible.

In addition, the electrolytic capacitor according to the embodimentbecomes resistive to destruction due to heat generated at the time ofshort circuit because of the PTC function of the main electrode layer14B, so that destruction caused by heat generated at the time of shortcircuit can be prevented as much as possible by using the PTC function.

The other configuration, operation, action, effect, and modification ofthe electrolytic capacitor according to the third embodiment and theother procedure, action, effect, and modification of the electrolyticcapacitor manufacturing method of the third embodiment are similar tothose of the first embodiment.

Fourth Embodiment

A fourth embodiment of the invention will now be described.

FIGS. 12 and 13 show the configuration of an electrolytic capacitoraccording to a fourth embodiment. FIG. 12 shows an externalconfiguration corresponding to FIG. 1, and FIG. 13 shows a sectionalconfiguration (of a section taken along line XIII—XIII of FIG. 12)corresponding to FIG. 2. The electrolytic capacitor of the fourthembodiment has a structure similar to that of the electrolytic capacitorof the first embodiment (refer to FIGS. 1 to 3) except for the pointthat a PTC layer 30 having the PTC function is connected to the cathode14.

The electrolytic capacitor according to the fourth embodiment has astructure in which, for example, as shown in FIGS. 12 and 13, an anodelead 21 and a cathode lead 22 are connected to the capacitor element 10and the periphery of the capacitor element 10 is covered with a moldresin (not shown) so that both of the anode lead 21 and the cathode lead22 are partially exposed. In the electrolytic capacitor, for example,the PTC layer 30 is connected to the cathode 14 via a conductiveadhesive 41, and the cathode lead 22 is connected to the PTC layer 30via a conductive adhesive 42.

The cathode 14 in the electrolytic capacitor according to the embodimenthas, for example, a two-layer structure in which the sub electrode layer14A and the main electrode layer 14B are stacked in this order and doesnot have the PTC function.

The PTC layer 30 is a resistance control layer having the PTC function.The PTC layer 30 has a sheet-shaped structure in which the conductiveparticles are held in the high polymer and is a so-called polymer PTC(P-PTC) layer. The high polymer of the PTC layer 30 is, for example, athermosetting high polymer and a thermoplastic high polymer. Concreteexamples of the thermosetting high polymers are epoxy resin, unsaturatedpolyester resin, polyimide, polyurethane, phenol resin, and siliconeresin. Examples of the thermoplastic resins are olefin polymers (such aspolyethylene, ethylene-vinylacetate copolymer, and polyalkylacrylate),halogen polymers (such as fluorine polymers (polyvinylidene fluoride,polytetrafluoroethylene, polyhexafluoropropylene, and copolymers ofthem), chlorine polymers (such as chlorinated polyethylene), polyamide,polystyrene, polyalkylene oxide, and thermoplastic polyester. Conductiveparticles are metal particles of nickel (Ni), copper (Cu), aluminum(Al), tungsten (W), molybdenum (Mo), zinc (Zn), cobalt (Co), platinum(Pt), gold (Au), silver (Ag), and the like, conductive ceramic particlesof tungsten carbide (WC), titanium nitride (TiN), zirconium nitride(ZrN), titanium carbide (TiC), titanium boride (TiB₂), molybdenumsilicide (MoSi₂), and tantalum boride (TaB₂), or carbon particles suchas carbon black (C).

The PTC layer 30 having the sheet structure has an bottom face M1 (firstface) on the side close to the cathode 14 and a top face M2 (secondface) on the side far from the cathode 14 (on the side close to thecathode lead 22). Surface process for exposing the conductive particlesare performed on at least one of the bottom face M1 and the top face M2of the PTC layer 30. In the PTC layer 30, for example, the surfaceprocess is performed on only the bottom face M1. The surface process isat least one of, for example, plasma process, ultraviolet process, ozoneprocess, and laser process. The bottom face M1 of the PTC layer 30 iselectrically connected to the cathode 14 via the conductive adhesive 41,and the top face M2 of the PTC layer 30 is electrically connected to thecathode lead 22 via the conductive adhesive 42. The details of thesurface structure of the bottom face M1 of the PTC layer 30 subjected tothe surface process will be described in detail later (refer to FIG.14).

The conductive adhesive 41 is a first conductive adhesive forelectrically connecting the PTC layer 30 to the cathode 14 and is, forexample, a paste adhesive containing a metal (such as silver (Ag)). Theconductive adhesive 42 is a second conductive adhesive for electricallyconnecting the PTC layer 30 to the cathode lead 22 and is, for example,an adhesive similar to the conductive adhesive 41.

Both of the anode lead 21 and cathode lead 22 are electrode leads forpassing current to the capacitor element 10. The anode lead 21 andcathode lead 22 are made of, for example, a metal such as iron (Fe) orcopper (Cu) or a plated metal obtained by plating the metals (forexample, tin (Sn) plating or tin lead (SnPb) plating) and are connectedto the anode 11 and the cathode 14, respectively, in the capacitorelement 10.

Referring now to FIG. 14, the detailed configuration of the electrolyticcapacitor will be described. FIG. 14 shows a partially enlargedsectional configuration of the electrolytic capacitor shown in FIG. 13.

In the PTC layer 30, as described above, the surface process forexposing the conductive particles is performed on the bottom face M1.Concretely, for example, as shown in FIG. 14, in the bottom face M1 ofthe PTC layer 30, a high polymer 32 is partially removed along theconductive particles 31 around the conductive particles 31 distributednear the bottom face M1, and a recess 30K is formed as an area fromwhich the high polymer 32 is partially removed. The conductive particles31 are connected to each other in an almost line shape in the highpolymer 32, thereby forming a chain of a current path (so-calledconductive path). In particular, in the PTC layer 30, for example, todecrease the contact resistance between the PTC layer 30 and the cathode14 by increasing the contact area (electric contact area) between theconductive particles 31 and the conductive adhesive 41, the recess 30Kis formed by partially removing the high polymer 32 so that removaldepth D reaches about ⅓ or more of the particle diameter (averageparticle diameter) S of the conductive particle 31. In FIG. 14, only theconductive particles 31 distributed around the bottom face M1 of the PTClayer 30 out of the conductive particles 31 held in the high polymer 32are shown.

In the electrolytic capacitor shown in FIGS. 12 to 14, by passingcurrent to the capacitor element 10 via the anode lead 21 and thecathode lead 22, charges are accumulated in the capacitor element 10. Atthis time, by using the PTC layer 30 having the PTC function,destruction of the electrolytic capacitor due to heat generated at thetime of short circuit is prevented. Specifically, when overvoltage orbackward voltage is applied to the electrolytic capacitor, if thedielectric layer 12 is partially damaged and short circuit occurs, dueto this, excess current flows among the anode 11, solid electrolytelayer 13, and cathode 14, and heat is generated. Due to the heatgenerated at the time of short circuit, the temperature of the PTC layer30 rises and the resistance exponentially increases. As a result, theexcess current flowing in the capacitor element 10 is suppressed, sothat destruction of the capacitor element 10 caused by the excesscurrent is suppressed. The factors of the rise in the temperature of thePTC layer 30 are, for example, the generation of heat at the time ofshort circuit and also the Joule's heat caused by excess current. Whenthe temperature of the PTC layer 30 decreases after that, the resistanceof the PTC layer 30 decreases as the temperature decreases.Consequently, the capacitor element 10 is reset to an energizable state.The principle that the PTC layer 30 has the PTC function is similar tothat described in the foregoing first embodiment (the principle that themain electrode layer 14B has the PTC function).

Referring now to FIGS. 12 to 15, as the electrolytic capacitormanufacturing method according to the embodiment, the electrolyticcapacitor manufacturing method shown in FIG. 3 and FIGS. 12 to 14 willbe described. FIG. 15 is provided to describe the flow of amanufacturing process of the electrolytic capacitor manufacturingmethod. In the following, since the materials of the components of theelectrolytic capacitor have been already described in detail, thedescription will not be repeated.

The electrolytic capacitor manufacturing method of the fourth embodimentis similar to that of the first embodiment (refer to FIG. 4) except forthe point that a process of forming the cathode 14 having no PTCfunction and connecting the PTC layer 30 to the capacitor element 10 isnewly added. At the time of manufacturing the electrolytic capacitor,first, the capacitor element 10 shown in FIG. 3 and FIGS. 12 to 14 isformed. Specifically, first, valve metal foil subjected to the surfaceenlarging process is prepared (step S601 in FIG. 15), the dielectriclayer 12 is formed so as to partially cover the periphery of the anode11 (step S602 in FIG. 15), the solid electrolyte layer 13 is formed soas to cover the dielectric layer 12 (step S603 in FIG. 15) and,subsequently, the cathode 14 is formed so as to cover the periphery ofthe solid electrolyte layer 13 (step S604 in FIG. 15). At the time offorming the cathode 14, for example, by applying and drying a carbonpaste around the solid electrolyte layer 13, the sub electrode layer 14Ais formed. A silver paste is applied on the sub electrode layer 14A anddried, thereby forming the main electrode layer 14B. In such a manner,the cathode 14 having the stacked structure in which the sub electrodelayer 14A and the main electrode layer 14B are stacked in this order isformed. As a result, the capacitor element 10 having the stackedstructure in which the anode 11, dielectric layer 12, solid electrolytelayer 13, and cathode 14 are stacked in this order is completed (referto FIGS. 3, 12, and 13).

Subsequently, the PTC layer 30 having the PTC function is connected tothe capacitor element 10 (cathode 14) (step S605 in FIG. 15).

An example of the procedure of connecting the PTC layer 30 is asfollows. First, a high polymer containing conductive particles is formedin a sheet shape, thereby preparing the PTC layer 30 having a sheetstructure (step S6051). Subsequently, surface process for exposing theconductive particles is performed on at least one of the bottom face M1facing the cathode 14 in the PTC layer 30 and the top face M2 on theside opposite to the bottom face M1 (step S6052). At the time ofperforming the surface process, for example, the surface process isperformed only to the bottom face M1 of the PTC layer 30. As the surfaceprocess, at least one of plasma process, ultraviolet process, ozoneprocess, and laser process is performed. Concretely, by performing thesurface process on the bottom face M1 of the PTC layer 30, for example,as shown in FIG. 14, the high polymer 32 is partially removed along theconductive particles 31, thereby forming the recess 30K as the area fromthe high polymer 32 is partially removed. In this case, particularly,for example, to decrease the contact resistance between the PTC layer 30and the cathode 14 by increasing the contact area (electric contactarea) between the conductive particles 31 and the conductive adhesive41, it is preferable to partially remove the high polymer 32 so that theremoval depth D reaches about ⅓ or more of the particle diameter(average particle diameter) S of the conductive particles 31. Finally,the bottom face M1 subjected to the surface process, of the PTC layer 30is bonded to the cathode 14 by using the conductive adhesive 41 (stepS6053). As a result, the PTC layer 30 is electrically connected to thecathode 14 via the conductive adhesive 41.

An example of the process of the surface process is as follows.

First, in the case of using the plasma process as the surface process,for example, discharge gas is introduced into a vacuum vessel togenerate plasma. By using ion bombardment of the plasma and activeoxidizing gas formed in the plasma, the high polymer 32 can be partiallyremoved. As the discharge gas, for example, an inactive gas of argon(Ar) or the like, an oxidizing gas of oxygen (O₂) or the like, or amixture gas of the inactive gas and oxidizing gas can be used. Concreteexamples of the plasma process are reactive ion etching process usingthe oxidizing gas as the discharge gas and reverse sputtering processusing an inactive gas as the discharge gas.

Second, in the case of using the ultraviolet process as the surfaceprocess, for example, by emitting an ultraviolet ray to cut atoms.coupled in. the high polymer 32, the high polymer 32 can be partiallyremoved. In this case, for example, by performing the ultravioletemitting process in an oxidizing atmosphere, a decomposed matter whichis generated at the time of removing the high polymer 32 can be oxidizedand removed by the oxidizing gas. For example, by performing ultravioletray irradiating process in an inactive gas atmosphere and water-washingor etching the processed high polymer 32, a decompressed matter which isgenerated at the time of removing the high polymer 32 can be removed.

Third, in the case of using the ozone process as the surface process,for example, by making the high polymer 32 exposed in an ozoneatmosphere to make direct reaction, the high polymer 32 can be partiallyremoved by using the oxidizing reaction of the ozone having strongoxidizing power. It is not limited to use only one of the ultravioletprocess and the ozone process but may use both of the ultravioletprocess and the ozone process.

Fourth, in the case of using the laser process as the surface process,for example, by emitting a laser beam and using strong opticalexcitation reactivity of the laser beam, atoms coupled in the highpolymer 32 can be disconnected to thereby partially remove the highpolymer 32. The laser process is generally known as a laser abrasionmethod and is a kind of optical decomposition removing process.

Apparatuses, processing conditions, and the like used for carrying outthe series of surface processes can be freely set.

Finally, for example, by connecting the anode lead 21 to the anode 11 inthe capacitor element 10 and bonding the cathode lead 22 to the PTClayer 30 by using the conductive adhesive 42, the cathode lead 22 isconnected to the PTC layer 30 via the conductive adhesive 42 (step S606in FIG. 15). After that, the periphery of the capacitor element 10 iscovered with a mold resin so that both of the anode lead 21 and thecathode lead 22 are partially exposed (step S607 in FIG. 15). As aresult, the electrolytic capacitor having the structure in which theanode lead 21 and the cathode lead 22 are connected to the capacitorelement 10 and the periphery of the capacitor element 10 is covered witha mold resin so that both of the anode lead 21 and the cathode lead 22are partially exposed is completed.

In the electrolytic capacitor manufacturing method of the embodiment,the PTC layer 30 having the PTC function is connected to the cathode 14,so that the PTC function is given to the electrolytic capacitor by thePTC layer 30 on the basis of the principle of the PTC function. In thiscase, specifically, the surface process for exposing the conductiveparticles is performed on the bottom face M1 of the PTC layer 30 and,after that, the bottom face M1 subjected to the surface process, of thePTC layer 30 is connected to the cathode 14, thereby exposing theconductive particles 31 in the bottom face M1 of the PTC layer 30 asshown in FIG. 14. Consequently, as shown in FIG. 16, as compared withthe case where the PTC layer 30 is connected to the cathode 14 withoutperforming the surface process on the bottom face M1, that is, in thecase where the conductive particles 31 are not exposed in the bottomface M1 of the PTC layer 30, the contact area (electric contact area)between the PTC layer 30 (conductive particles 31) and the cathode 14increases, so that contact resistance between the PTC layer 30 and thecathode 14 decreases. As a result, while preventing destruction of theelectrolytic capacitor caused by heat generated at the time of shortcircuit by using the PTC function, the resistance characteristic of theelectrolytic capacitor can be decreased. Therefore, the resistancecharacteristic of the electrolytic capacitor having the PTC function canbe reduced as much as possible.

In the embodiment, the bottom face M1 of the PTC layer 30 is connectedto the cathode 14 by using the conductive adhesive 41, as shown in FIG.14, by the surface process, the recess 30K formed in the bottom face M1of the PTC layer 30 is sufficiently filled with the conductive adhesive41. In this case, for example, as compared with the case where thebottom face M1 of the PTC layer 30 subjected to the surface process isbonded to the cathode 14 by thermo compression, the contact area betweenthe conductive particles 31 and the conductive adhesive 41 increases. Asa result, the electric connection area between the conductive particles31 and the cathode 14 increases, so that the contact resistance betweenthe PCT layer 30 and the cathode 14 remarkably decreases. Therefore, theresistance characteristic of the electrolytic capacitor having the PTCfunction can be reduced more.

In the embodiment, as shown in FIG. 14, by performing the surfaceprocess on the bottom face M1 of the PTC layer 30, at the time ofpartially removing the high polymer 32, the high polymer 32 is partiallyremoved until the removal depth D reaches ⅓ or more of the particlediameter (average particle diameter) S of the conducive particle 31.Consequently, the specific conductive particles 31 distributed aroundthe bottom face M1 are sufficiently exposed in the recess 30K, that is,the exposure area of the conductive particles 31 constructing the mainelectric connection path between the PTC layer 30 and the cathode 14 isassured. Therefore, from the viewpoint as well, the electric connectionarea between the conductive particles 31 and the cathode 14 increases,so that the resistance characteristic of the electrolytic capacitorhaving the PTC function can be further reduced.

In addition to the above, in the electrolytic capacitor of theembodiment, while assuring the PTC function in the PTC layer 30, thecontact resistance between the PTC layer 30 and the cathode 14 isreduced. Therefore, the PTC function can be assured while reducing theresistance as much as possible.

Although the surface process is performed on only the bottom face Ml ofthe PTC layer 30 in the embodiment, the invention is not always limitedto the embodiment. For example, as shown in FIGS. 17 and 18, the surfaceprocess may be performed on both of the bottom face M1 and the top faceM2 of the PTC layer 30. FIG. 17 is provided to describe a modificationof the electrolytic capacitor manufacturing method and shows the flow ofthe manufacturing process corresponding to FIG. 15. FIG. 18 shows apartially enlarged sectional configuration of the electrolytic capacitorcorresponding to FIG. 14. In the electrolytic capacitor manufacturingmethod, as shown in FIGS. 3, 12, 13, 17, and 18, the anode 11 isprepared (step S701), the dielectric layer 12, solid electrolyte layer13, and cathode 14 are formed on the anode 11 (steps S702, S703, andS704), and the PTC layer 30 subjected to the surface process isconnected to both of the bottom face M1 and the top face M2 of the solidelectrolyte layer 13 by using the conductive adhesive 41 (step S705).Concretely, first, the sheet-shaped PTC layer 30 in which the conductiveparticles are held in the high polymer is prepared (step S7051).Subsequently, by performing the surface process on both of the bottomface M1 and the top face M2 of the PTC layer 30 (step S7052), the recess30K is formed by partially removing the high polymer 32 in both of thebottom face M1 and the top face M2 as shown in FIG. 18 to thereby exposethe conductive particles 31. The kind of the process used as the surfaceprocess and the procedure of the surface process are, for example,similar to those of the foregoing embodiment. Finally, the bottom faceM1 subjected to the surface process of the PTC layer 30 is bonded to thecathode 14 by using the conductive adhesive 41 (step S7053). In such amanner, the PTC layer 30 is electrically connected to the cathode 14 viathe conductive adhesive 41. After that, the anode lead 21 is connectedto the anode 11 in the capacitor element 10 and the cathode lead 22 isbonded to the PTC layer 30 by using the conductive adhesive 42, therebyconnecting the cathode lead 22 to the PTC layer 30 via the conductiveadhesive 42 (step S706). After that, the periphery of the capacitorelement 10 is covered with a mold resin so that both of the anode lead21 and the cathode lead 22 are partially exposed (step S707), therebycompleting the electrolytic capacitor. In this case, by the action basedon the surface process described in the foregoing embodiment, theconductive particles 31 are exposed in the bottom face M1 of the PTClayer 30. Consequently, the contact resistance between the PTC layer 30and the cathode 14 decreases and the conductive particles 31 are exposedalso in the top face M2, so that the contact resistance between the PTClayer 30 and the cathode lead 22 also decreases. Since the contactresistance decreases between the PTC layer 30 and the cathode 14 andbetween the PTC layer 30 and the cathode lead 22, as compared with thecase of the foregoing embodiment in which the surface process isperformed on only the bottom face M1 of the PCT layer 30, the resistancecharacteristic of the electrolytic capacitor can be further decreased.The procedure other than the above-described procedure of theelectrolytic capacitor manufacturing method shown in FIG. 17 and thecharacteristics other than the above-described characteristics of theelectrolytic capacitor shown in FIG. 18 are, for example, similar tothose shown in FIGS. 15 and 14.

Obviously, in the embodiment, as shown in FIG. 19, the surface processmay be performed on only the top face M2 without performing the surfaceprocess on the bottom face M1 of the PTC layer 30. In this case as well,the contact resistance between the PTC layer 30 and the cathode lead 22decreases, so that effects similar to those of the foregoing embodimentcan be obtained. The characteristics other than the above-describedcharacteristics of the configuration of the electrolytic capacitor shownin FIG. 19 are, for example, similar to those of the case shown in FIG.18 except for the point that the surface process is not performed on thebottom face M1. The method of manufacturing the electrolytic capacitorshown in FIG. 19 is, for example, similar to that of the case shown inFIG. 17 except for the point that the surface process is not performedon the bottom face M1 of the PTC layer 30.

Although the PTC layer 30 is bonded to the cathode 14 by using theconductive adhesive 41 at the time of connecting the PTC layer 30 to thecathode 14 in the embodiment, the invention is not always limited to theembodiment. The PTC layer 30 may be bonded to the cathode 14 by using,for example, a bonding method such as thermo compression bonding inplace of using the conductive adhesive 41. In this case as well, effectssimilar to those of the foregoing embodiment can be obtained. In thecase of bonding the PTC layer 30 to the cathode 14, it should be notedthat, for example, if an excessive external force is applied to thecapacitor element 10 at the time of bonding, the thin dielectric layer12 is easily broken due to the external force.

The other configuration, operation, action, effect, and modification ofthe electrolytic capacitor according to the fourth embodiment and theother procedure, action, effect, and modification of the electrolyticcapacitor manufacturing method of the fourth embodiment are similar tothose of the first embodiment.

EXAMPLES

Concrete examples of the invention will now be described.

An electrolytic capacitor was manufactured by using an electrolyticcapacitor manufacturing method described in the first embodiment.Specifically, first, a sintered body (tantalum sintered body) oftantalum powders in which an anode lead made of copper is buried wasprepared as an anode. A voltage (5V) was applied to the tantalumsintered body in a formation solution so that the anodizing reactionprogresses, thereby forming a dielectric layer. A monomer solution inwhich monomer, dopant, and oxidizer are dispersed in a solvent wasprepared, and the anode in which the dielectric layer was formed wasdipped in the monomer solution for 30 seconds, thereby making themonomer solution adhered on the surface of the dielectric layer. Afterthat, the anode was taken out at 0.5 mm/second and dried at roomtemperature. Subsequently, the anode dipped in the monomer solution wasput in a drier (with the temperature of 95° C.) and heated. The monomerwas oxidation-polymerized by using the oxidizer contained in the monomersolution, thereby forming a solid electrolyte layer so as to include aconductive high polymer doped with the dopant. A sub electrode layer wasformed so as to cover the solid electrolyte layer. After that, a mainelectrode layer was formed so as to cover the sub electrolytic layer,thereby forming the cathode having the PTC function so as to have thetwo-layered structure including the sub electrode layer and the mainelectrode layer. In this case, as the PTC function of the cathode, theresistance was set to be higher (than that of resistance at roomtemperature) by about 100,000 times or more in the temperature range of120° C. to 150° C. As a result, a capacitor element having a stackedstructure in which the anode, dielectric layer, solid electrolyte layer,and cathode (sub electrode layer and main electrode layer) are stackedin this order was formed. Finally, a cathode lead made of copper wasconnected to the capacitor element by using a conductive adhesive(silver adhesive) and, after that, the periphery of the capacitorelement was covered with epoxy resin as a mold resin so that the anodeand cathode leads are partially exposed, thereby completing theelectrolytic capacitor.

The procedure of forming the solid electrolyte layer is as follows.First, 3,4-ethylenedioxythiophene (“Baytron M” (trademark) of BayerLtd.) as a monomer and a para-toluenesulfonic acid iron (III) 50%butanol solution (“Baytron C” (trademark) of Bayer Ltd.) as a dopant andoxidizer were sufficiently cooled with ice water. 0.867 g of the monomerand 10.4 g of the dopant and oxidizer were weighed. While cooling themonomer and the dopant and oxider with ice water, they were mixed andstirred with a magnetic stirrer, thereby preparing the monomer solution.Subsequently, the anode in which the dielectric layer was already formedwas dipped in the monomer solution, thereby making the monomer solutionapplied onto the surface of the dielectric layer. The dielectric layeron which the monomer solution was applied was left at room temperaturefor about one hour. After that, the monomer solution was heated tooxidization-polymerize the monomer, thereby forming polyethylenedioxythiophene as the conductive high polymer so as to cover thedielectric layer. The heating parameters were that heatingtemperature=100° C. and heating time=15 minutes. Finally, bysufficiently cleaning the conductive high polymer with distilled water,unpolymerized monomer, excessive dopant, used oxidizer, and the likewere washed away, and the conductive high polymer was dried. At the timeof forming the conductive high polymer, the procedure of generating theconductive high polymer was repeated three times. Each time theoxidation polymerization completed, the conductive high polymer waswashed with distilled water or ethanol, thereby removing theunpolymerized monomer, excessive dopant, and used oxidizer. In such amanner, a solid electrolyte layer containing the conductive high polymerwas formed.

Electrolytic capacitors (examples 1-1 to 1-3) were manufactured whilechanging the configuration of the cathode (sub electrode layer and mainelectrode layer) having the PTC function by using the above-describedelectrolytic capacitor manufacturing method. After that, thecharacteristics of the electrolytic capacitors were examined. At thetime of examining the characteristics of the electrolytic capacitors ofthe invention, to evaluate the performances by comparison, a comparativeelectrolytic capacitor (comparative example 1) with the configurationdescribed below was manufactured and its characteristics were alsoexamined.

Example 1-1

A cathode was formed by the following procedure so that only a mainelectrode layer has the PTC function. Specifically, carbon black (CB)paste TC-8263 of Tanaka Kikinzoku Kogyo K. K. was used as the material(carbon paste) of a sub electrode layer. The carbon paste was applied onthe surface of a solid electrolyte layer and dried at 125° C., therebyforming the sub electrode layer. A conductive high polymer sheet wasmanufactured by forming a mixed material containing the high polymer andconductive particles in a sheet shape and was connected to the surfaceof the sub electrode layer, thereby forming a main electrode layer. Atthe time of forming the conductive high polymer sheet, polyvinylidenefluoride (PVDF) Kynar7201 (melting point=122° C. to 126° C., specificgravity=1.88) of Atofina Chemicals was used as the high polymer, andfilament nickel powder (Ni) type 210 (average particle diameter=0.5 μmto 1.0 μm, apparent density=0.80 g/cm³, specific surface area=1.50 m²/gto 2.50 m²/g, addition capacity ratio (high polymer : conductiveparticles)=65:35) of INCO Limited was used as the conductive particles.The high polymer and conductive particles were melted and kneaded in akneading mill of 150° C. The kneaded material was thermal-pressed so asto be formed in a sheet shape having a thickness of about 0.2 mm,thereby manufacturing a conductive high polymer sheet. As the process ofconnecting the conductive high polymer sheet, a thermo compressionbonding process was used.

Example 1-2

A cathode was formed by a procedure similar to that of Example 1-1except for the point that a conductive high polymer sheet wasmanufactured by using linear low-density polyethylene (L-LDPE) UJ960(melting point=127° C. and specific gravity=0.921) of Japan PolyethyleneCorporation as the high polymer and using titanium carbide (TiC) TiC-01(average particle diameter=0.9 μm to 1.5 μm, addition capacity ratio(high polymer: conductive particles=68:32)) of Japan New Metals Co.,Ltd. as the conductive particles.

Example 1-3

A cathode was formed by the following procedure so that only a subelectrode layer has the PTC function. A conductive high polymer sheetwas manufactured by forming a mixed material containing the high polymerand conductive particles in a sheet shape and was connected to thesurface of a solid electrolyte layer, thereby forming a sub electrodelayer. At the time of forming the conductive high polymer sheet, highdensity polyethylene (HDPE) HY540 (melting point=135° C. and specificgravity=0.961) of Japan Polyethylene Corporation was used as the highpolymer and carbon black (CB) Raven430 (addition capacity ratio (highpolymer: conductive particles)=67:33) of Columbian Chemicals Company wasused as the conductive particles. The high polymer and conductiveparticles were melted and kneaded in a kneading mill of 150° C. Thekneaded material was thermal-pressed so as to be formed in a sheet shapehaving a thickness of about 0.2 mm, thereby manufacturing a conductivehigh polymer sheet. As the process of connecting the conductive highpolymer sheet, a thermo compression bonding process was used. As thematerial (metal paste) of the main electrode layer, silver pasteNH-1429N of Tanaka Kikinzoku Kogyo K. K. was used. The silver paste wasapplied on the surface of the sub electrode layer and dried, therebyforming the main electrode layer.

Comparative Example 1

By the following procedure, a cathode was formed so as not to have thePTC function. As the material of a sub electrode layer, the carbon pasteused in Example 1-1 was used. The carbon paste was applied on thesurface of a solid electrolyte layer and dried at 125° C., therebyforming the sub electrode layer. The silver paste used in Example 1-3was used as the material of a main electrode layer. The silver paste wasapplied on the surface of the sub electrode layer and dried, therebyforming the main electrode layer.

Performance tests were conducted on the electrolytic capacitors of.Examples 1-1 to 1-3 and Comparative Example 1 to check the operationcharacteristics of the electrolytic capacitors. Table 1 shows theresult. Table 1 shows the operation characteristics of the electrolyticcapacitors. As “evaluation”, “good” or “bad” is shown. At the time ofexamining the operation conditions of the electrolytic capacitors,backward voltage (=30V) was applied to each of the electrolyticcapacitors and visual observation was carried out. When firing did notoccur, it was determined as “good”. When firing occurred, it wasdetermined as “bad”. For reference sake, Table 1 also shows theconstruction (high polymer and conductive particles) of the cathode (subelectrode layer and main electrode layer) and whether the PTC functionis provided for each of the sub and main electrode layers or not.

TABLE 1 Sub electrode layer Main electrode layer High Conductive PTCHigh Conductive PTC polymer particles function polymer particlesfunction Evaluation Example 1-1 CB paste Absence PVDF Ni Presence GoodExample 1-2 CB paste Absence L-LDPE TiC Presence Good Example 1-3 HDPECB Presence Silver paste Absence Good Comparative CB paste AbsenceSilver paste Absence Bad example 1

As understood from the result of Table 1, in the electrolytic capacitorsof Examples 1-1 and 1-2 in which the main electrode layer has the PTCfunction and the electrolytic capacitor of Example 1-3in which the subelectrode layer has the PTC function, although excess current(short-circuit current) flowed instantaneously due to occurrence ofshort circuit when the backward voltage is applied, the excess currentwas immediately suppressed by using the PTC function, so that no firingoccurred. The resistance change in the main electrode layer or subelectrode layer having the PTC function of each of the electrolyticcapacitors of Examples 1-1 to 1-3 was examined. The resistance increasedby 1,000 times or more as the temperature rises. The resistance changerate was sufficient to display the PTC function. On the other hand, inthe electrolytic capacitor having no PTC function of Comparative Example1, when backward voltage was applied, short circuit occurred and excesscurrent flowed. Since the electrolytic capacitor does not have the PTCfunction, when the excess current continuously flowed, heat wasgenerated and, finally, firing occurred. Therefore, it was recognizedthat in the electrolytic capacitors of Examples 1-1 to 1-3, by using thePTC function, destruction caused by heat generated at the time of shortcircuit can be prevented.

Although concrete data will not be presented, the characteristics of anelectrolytic capacitor manufactured so that both of the sub and mainelectrolytic layers have the PTC function, concretely, an electrolyticcapacitor obtained by replacing the sub electrolytic layer (without thePTC function) of Examples 1-1 and 1-2 with the sub electrolytic layer(with the PTC function) of Example 1-3 or an electrolytic capacitorobtained by replacing the main electrolytic layer (without the PTCfunction) of Example 1-3 with the main electrode layer (with the PTCfunction) of Examples 1-1 and 1-2 were examined. In any of theelectrolytic capacitors, results similar to those of the electrolyticcapacitors of Examples 1-1 to 1-3 were obtained. Thus, it was recognizedthat an electrolytic capacitor can be stably manufactured also in thecase where both of the sub and main electrolytic layers have the PTCfunction.

Next, an electrolytic capacitor was manufactured by using theelectrolytic capacitor manufacturing method of the second embodiment.First, as the anode, aluminum foil subjected to a process (surfaceenlarging process) was prepared. Voltage (=23V) was applied to thealuminum foil in a formation solution to make anodic oxidation reactionprogressed to form an oxide aluminum film, thereby forming a dielectriclayer. After formation of the dielectric layer, capacity was measured inan adipic acid ammonium aqueous solution, and theoretical capacity wasabout 100 μF. Subsequently, a monomer solution obtained by dispersingmonomer, dopant, and oxidizer in a solvent was prepared. By dipping theanode in which the dielectric layer was already formed in the monomersolution for 30 seconds, the monomer solution was adhered onto thesurface of the dielectric layer. After that, the anode was taken out in0.5 mm/second and dried at room temperature. Subsequently, the anodealready dipped in the monomer solution was put in a drier and was heatedto oxidation-polymerize the monomer by using the oxidizer contained inthe monomer solution, thereby forming the solid electrolyte layer so asto contain the conductive high polymer doped with the dopant. Theprocedure of forming the solid electrolyte layer is similar to that ofthe case of manufacturing the electrolytic capacitor of the firstembodiment. Subsequently, by applying a carbon paste on the surface ofthe solid electrolyte layer and drying it, the sub electrode layer wasformed. Subsequently, the silver paste was applied on the surface of thesub electrode layer and dried, thereby forming the main electrode layer.After that, the auxiliary electrode layer having the PTC function wasformed so as to cover the main electrode layer, thereby forming thecathode having the PTC function so as to have the three-layer structureincluding the sub electrode layer, main electrode layer, and auxiliaryelectrode layer. As a result, the capacitor element having the stackedstructure in which the anode, dielectric layer, solid electrolyte layer,and cathode (sub electrode layer, main electrode layer, and auxiliaryelectrode layer) are stacked in this order was formed. Finally, an anodelead and a cathode lead made of copper were connected to the capacitorelement by using a conductive adhesive (silver adhesive) and theperiphery of the capacitor element was covered with an epoxy resin as amold resin so as to partially expose both of the anode and cathodeleads, thereby completing the electrolytic capacitor.

Electrolytic capacitors (Examples 2-1 to 2-7) of the invention weremanufactured while changing the configuration of the cathode (auxiliaryelectrode layer) having the PTC function by using the electrolyticcapacitor manufacturing method and, after that, the characteristics ofthe electrolytic capacitors were examined. At the time of examining thecharacteristics of the electrolytic capacitors of the invention, tocompare and evaluate the performances, comparative electrolyticcapacitors (Comparative Examples 2-1 to 2-4) were also manufacturedwhile changing the configuration of the cathode and the characteristicsof the electrolytic capacitors were also examined.

Example 2-1

As the material (metal paste) of an auxiliary electrode layer, a mixture(epoxy resin α: mixing weight ratio of (EPICLON850:EP4005)=75:25)between an epoxy resin EPICLON850 (epoxy equivalent=190 g/eq) ofDainippon Ink and Chemicals, Incorporated and an epoxy resin EP4005(epoxy equivalent=510 g/eq) of Asahi Denka Co., Ltd. was used. As theconductive particles, metal particles, concretely, filament nickelpowders (Ni) Type 255 (average particle diameter=2.2 μm to 2.8 μm,apparent density=0.50 g/cm³ to 0.65 g/cm³, specific surface area=0.68m²/g, addition capacity ratio (high polymer : conductiveparticles=40:60) of INCO Limited were used. A metal paste was applied onthe surface of the main electrode layer and was set at 130° C. undernitrogen atmosphere, thereby forming an auxiliary electrode layer so asto have the thickness of 0.3 mm. As the metal paste, a metal pastecontaining the liquid high polymer and conductive particles and, as aco-hardener, a hardener B570 (acid anhydride equivalent=168 g/eq,equivalent ratio between acid anhydride and liquid high polymer=1:1) ofDainippon Ink and Chemicals, Incorporated and a hardening acceleratorPN-40J (addition amount=1% by weight of the weight of the liquid highpolymer) of Ajinomoto-Fine-Techno Co., Inc. was used.

Example 2-2

An auxiliary electrode layer was formed by a procedure similar to thatof Example 2-1 except for the point that an epoxy resin (epoxy resin β)AK-601 (epoxy equivalent=153 g/eq) of Nippon Kayaku Co., Ltd. was usedin place of the epoxy resin α as the liquid high polymer (film-statehigh polymer).

Example 2-3

An auxiliary electrode layer was formed by a procedure similar to thatof Example 2-1 except for the point that conductive ceramic particles,concretely, tungsten carbide (WC) WC-F (particle diameter=0.62 μm,addition capacity ratio (liquid high polymer: conductiveparticles)=70:30) of Japan New Metals Co., Ltd. was used in place of themetal particles as the conductive particles.

Example 2-4

As the liquid high polymer (film high polymer), a soluble thermoplastichigh polymer, concretely, polyvinylidene fluoride (PVDF; PVDFα)Kynar7201 (melting point=122° C. to 126° C., specific gravity=1.88) ofAtofina Chemicals dissolved in a mixture solvent of acetone and toluenewas used. As the conductive particles, conductive ceramic particles,concretely, tungsten carbide (WC; addition capacity ratio (liquid highpolymer: conductive particles)=70:30) used in Example 2-3 was used. Ametal paste prepared by stirring conductive particles in liquid highpolymer by a ball mill was applied on the surface of a main electrodelayer and dried in vacuum at 100° C., thereby forming an auxiliaryelectrode layer so as to have a thickness of 0.3 μm.

Example 2-5

An auxiliary electrode layer was formed by a procedure similar to thatof Example 2-4 except for the point that tantalum boride (TaB₂) TaB₂ ⁻O(particle diameter=1.00 μm, addition capacity ratio (liquid highpolymer: conductive particles)=68:32) of Japan New Metals Co., Ltd. wasused as the conductive particles in place of tungsten carbide.

Example 2-6

As the liquid high polymer (film high polymer), a soluble thermoplastichigh polymer, concretely, polyvinylidene fluoride (PVDF; PVDFβ) THV200P(melting point=115° C. to 125° C., specific gravity=1.91) of Sumitomo 3MLimited dissolved in N-methyl-2-pyrrolidone was used. As the conductiveparticles, metal particles, concretely, nickel powder used in Example2-1 was used. A metal paste prepared by stirring conductive particles inliquid high polymer by a ball mill was applied on the surface of a mainelectrode layer and dried in vacuum at 100° C., thereby forming anauxiliary electrode layer so as to have a thickness of 0.3 μm.

Example 2-7

An auxiliary electrode layer was formed by bonding a thermoplasticconductive high polymer sheet to the surface of a main electrode layerwithout using a metal paste as the material of the auxiliary electrodelayer. At the time of forming a conductive high polymer sheet, aninsoluble thermoplastic high polymer, concretely, high densitypolyethylene (HDPE) HY540 (melting point=135° C., specificgravity=0.961) of Japan Polyethylene Corporation was used. As theconductive particles, metal particles, concretely, filament nickelpowder type 210 (average particle diameter=0.5 μm to 1.0 μm, apparentdensity=0.80 g/cm³, specific surface area=1.50 m²/g to 2.50 m²/g,addition capacity ratio (high polymer: conductive particles)=65:35) ofINCO Limited was used. The high polymer and conductive particles weremelted and kneaded in a kneading mill of 150° C. The kneaded materialwas thermal-pressed so as to be formed in a sheet shape having athickness of about 0.2 mm. At the time of bonding the conductive highpolymer sheet to the surface of the main electrode layer, the conductiveadhesive Dotite XA-874 of Fujikurakasei Co., Ltd was used.

Comparative Example 2-1

An auxiliary electrode layer was formed by a procedure similar to thatof Example 2-7 except for using, as the conductive particles, in placeof the metal particles (nickel powder), carbon particles, concretely,carbon black (CB) #4500 TOKABLACK (particle diameter=40 nm, DBPabsorption number=168 cc/100 g, specific surface area=58 m²/g, additioncapacity ratio (non-liquid high polymer: conductive particles)=68:32) ofTokai Carbon Co., Ltd.

Comparative Example 2-2

An auxiliary electrode layer was formed by a procedure similar to thatof Comparative Example 2-1 except for the point that the conductive highpolymer sheet was not bonded to the surface of the main electrode layerbut was thermo-compression bonded by thermal press at 150° C.

Comparative Example 2-3

A polyvinylidene fluoride (PVDFα) used as a liquid high polymer (filmhigh polymer) in Example 2-4 was used as the material (metal paste) ofthe auxiliary electrode layer, carbon particles used in ComparativeExample 2-1 were also used as conductive particles, and a metal pasteprepared by stirring conductive particles in liquid high polymer by aball mill was applied onto the surface of a main electrode layer anddried in vacuum at 100° C., thereby forming an auxiliary electrode layerso as to have a thickness of 0.3 μm.

Comparative Example 2-4

A cathode was formed without forming an auxiliary electrode layer havingthe PTC function, specifically, so as to include only the sub electrodelayer and the main electrode layer having no PTC function.

The characteristics of the electrolytic capacitors of Examples 2-1 to2-7 and Comparative Examples 2-1 to 2-4 were examined and the resultshown in Table 2 was obtained. Table 2 shows the characteristics of theelectrolytic capacitors, which are “ESR (Equivalent Series ResistancemΩ)”, “leak current (μA”, and “backward voltage test”. As “ESR”, an ESRvalue of 100 kHz of each of the electrolytic capacitors measured byusing an impedance analyzer is shown. As the “leak current”, a leakcurrent value measured after application of voltage (=6.3V) to each ofthe electrolytic capacitors for five minutes is shown. As the “backwardvoltage test”, at the time of applying a backward voltage (=60V) to eachof the electrolytic capacitors, “bad” is written when a trouble (such asfiring, smoke, or the like) is observed and “good” is written when notrouble is observed. For reference sake, in Table 2, the material (theliquid high polymer (film high polymer) and conductive particles) of theauxiliary electrode layer, the presence/absence of the PTC function, andthe auxiliary electrode layer forming method are also shown.

TABLE 2 Leak Liquid high polymer Conductive PTC ESR current Backward(film high polymer) particles function Forming method (mΩ) (μA) voltagetest Example 2-1 Epoxy resin α Ni Presence Coating (hardening) 48.8 3.5Good Example 2-2 Epoxy resin β Ni Presence Coating (hardening) 47.2 4.3Good Example 2-3 Epoxy resin α WC Presence Coating (hardening) 53.4 5.2Good Example 2-4 PVDF α WC Presence Coating (drying) 56.2 3.1 GoodExample 2-5 PVDF α TaB₂ Presence Coating (drying) 59.8 5.5 Good Example2-6 PVDF β Ni Presence Coating (drying) 43.6 4.9 Good Example 2-7Conductive high polymer sheet Presence Bonding (adhesion) 82.1 4.7 GoodComparative Conductive high polymer sheet Presence Bonding (adhesion)162.0 5.8 Good example 2-1 Comparative Conducive high polymer sheetPresence Bonding (thermo 213.0 750.0 Good example 2-2 compressionbonding) Comparative PVDF α CB Presence Coating (drying) 151.0 7.2 Goodexample 2-3 Comparative — Absence — 35.0 1.2 Bad example 2-4

As understood from Table 2, if conditions (suitable conditions) suchthat the ESR is 100 mΩ or less, leak current is 10.0 μA or less, and thebackward voltage test is “good” have to be satisfied as characteristicsfor practical use of an electrolytic capacitor, the electrolyticcapacitors of Examples 2-1 to 2-7 using the metal particles orconductive ceramic particles as the conductive particles satisfy thesuitable conditions of all of the ESR, leak current, and backwardvoltage test. Specifically, firing, smoke, and the like did not occur inthe electrolytic capacitors of Examples 2-1 to 2-7 for the reasons: (1)since the metal particles or conductive ceramic particles are containedas the conductive particles, the ESR is suppressed because of the lowresistance characteristic of the metal particles or conductive ceramicparticles, (2) since excessive external force is not applied to thedielectric layer during manufacture and the dielectric layer is noteasily broken due to a mechanical factor, leak current is suppressed,and (3) although excess current flows instantaneously when backwardvoltage is applied, the resistance of the cathode is increased by usingthe PTC function of an auxiliary electrode layer, and excess current issuppressed. On the other hand, the electrolytic capacitors ofComparative Examples 2-1 to 2-3 do not satisfy part of the ESR, leakcurrent, and backward voltage test. Concretely, the electrolyticcapacitors of Comparative Examples 2-1 and 2-3 satisfy the suitableconditions of both of the leak current and the backward voltage test butdo not satisfy the ESR. The electrolytic capacitor of ComparativeExample 2-2 satisfies the suitable condition of only the backwardvoltage test but does not satisfy the suitable conditions of the ESR andleak current. Specifically, since the electrolytic capacitors ofComparative Examples 2-1 to 2-3 do not contain the metal particles orconductive particles but contain the carbon particles as the conductiveparticles, due to the resistance characteristic of the carbon particles,all of the electrolytic capacitors did not satisfy the suitablecondition of the ESR. For reference sake, although the electrolyticcapacitor of Comparative Example 2-4 satisfies the suitable conditionsof ESR and leak current, due to no PTC function, smoke was generated inthe backward voltage test. It was consequently recognized that in theelectrolytic capacitors of Examples 2-1 to 2-7, both of the ESR and leakcurrent are suppressed, occurrence of a trouble such as firing and smokeis prevented and, particularly, the resistance characteristic of theelectrolytic capacitors can be reduced.

In particular, when the ESR of the electrolytic capacitors of Examples2-1 to 2-7 are compared with each other, the ESR in the electrolyticcapacitors of Examples 2-1 to 2-6 using the applying (hardening ordrying) process is lower than that in the electrolytic capacitor ofExample 2-7 using the bonding (attaching) process for forming theauxiliary electrode layer. Specifically, in the electrolytic capacitorsof Examples 2-1 to 2-6, the contact resistance between the mainelectrode layer and the auxiliary electrode layer is lower than that inthe electrolytic capacitor of Example 2-7, so that the ESR is reducedonly by the decrease in the contact resistance. From the above, it wasrecognized that the resistance characteristic in Examples 2-1 to 2-6 canbe further lowered.

Although concrete data will not be presented, in place of manufacturingan electrolytic capacitor so that only the auxiliary electrode layer ina cathode having a three-layer structure (sub electrode layer, mainelectrode layer, and auxiliary electrode layer) has the PTC function, anelectrolytic capacitor in which only the sub electrode layer has the PTCfunction, an electrolytic capacitor in which only the main electrodelayer has the PTC function, an electrolytic capacitor in which onlyarbitrary two layers out of the sub electrode layer, main electrodelayer, and auxiliary electrode layer have the PTC function, and anelectrolytic capacitor in which all of the sub electrode layer, mainelectrode layer, and auxiliary electrode layer have the PTC functionwere manufactured and their characteristics were similarly examined. Inthe electrolytic capacitors, results similar to those of theelectrolytic capacitors of Examples 2-1 to 2-7 were obtained. Thus, itwas recognized that, irrespective of the structure of the cathode, byforming the cathode so as to contain the metal particles or conductiveceramic particles as the conductive particles, the resistancecharacteristic of the electrolytic capacitor can be reduced.

For reference sake, the PTC characteristics of the cathodes of Examples2-1 to 2-7 and Comparative Examples 2-1 to 2-3 were examined and resultsshown in Table 3 were obtained. Table 3 shows the PTC characteristics ofthe cathodes. As the PTC characteristics, “room temperature resistance(mΩ)”, “operation start temperature (° C.)”, and “resistance change rate(the number of digits)” are shown. The “operation start temperature” istemperature indicative of a resistance value which is five times aslarge as the resistance value shown at 25° C. The “resistance changerate” indicates the number of digits of increase in resistance, that is,the number of digits “x” of the case where the relation of R2=10^(x)×R1is satisfied between the room temperature resistance R1 and theresistance R2 increased based on the PTC function. In the case ofexamining the PTC function, with respect to Examples 2-1 to 2-6 andcomparative example 2-3, a film was formed by using the material (metalpaste) of the auxiliary electrode layer so as to have a thickness of 0.2mm between two electrolytic nickel foil electrodes (having a thicknessof 25 μm), thereby forming a PTC sheet with an electrode. The PTC sheetwas punched in a disc shape having a diameter of 10 mm. After that, thePTC sheet with an electrode was put in a thermostat and resistance wasmeasured at every two degrees by a four-terminal method while increasingthe temperature at 2° C./min. within the range from 25° C. to 160° C.With respect to Example 2-7 and Comparative Examples 2-1 and 2-2, a PTCsheet with an electrode was manufactured by a procedure similar to thatof Examples 2-1 to 2-6 and Comparative Example 2-3 except for the pointthat a conductive high polymer sheet was thermo-compression-bondedbetween two electrolytic nickel foil electrodes, and resistance of thePTC sheet with the electrode was measured. For reference, Table 3 alsoshows the material of the auxiliary electrode layer (liquid high polymer(film high polymer), conductive particles).

TABLE 3 Resistance Liquid Resistance Operation start change rate highpolymer Conductive (mΩ) at temperature (the number of (film highpolymer) particles room temperature (° C.) digits) Example 2-1 Epoxyresin α Ni 1.2 125 5.5 Example 2-2 Epoxy resin β Ni 1.4 128 5.3 Example2-3 Epoxy resin α WC 2.0 119 4.9 Example 2-4 PVDF α WC 1.5 117 8.2Example 2-5 PVDF α TaB₂ 2.4 120 7.6 Example 2-6 PVDF β Ni 1.2 125 8.7Example 2-7 Conductive high polymer sheet 0.7 127 9.0 ComparativeConductive high polymer sheet 27.2 126 5.2 examples 2-1, 2-2 ComparativePVDF α CB 29.7 124 5.1 example 2-3

As understood from the results shown in Table 3, in all of the cathodesof Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-3, theresistance change rate of three or more digits is obtained, that is, theresistance increased by 1,000 times or more. Consequently, it wasrecognized that the cathodes of Examples 2-1 to 2-7 and ComparativeExamples 2-1 to 2-3 have the resistance change rate sufficient todisplay the PTC function. Although concrete data will not be presented,for confirmation, the resistance characteristics of a carbon black pastehaving no PTC function (the sub electrode layer of Examples 2-1 to 2-7and Comparative Examples 2-1 to 2-3) and a silver paste having no PTCfunction (the main electrode layer of Examples 2-1 to 2-6 andComparative Examples 2-1 to 2-3) were examined, concretely, each of thepastes was formed in a film (by heating and drying) on a glass platehaving a size of 30 mm×30 mm by using the dipping method and, afterthat, room temperature resistance of each of the pastes was measured byusing a metal clip. Similarly, the resistance of each of the pastes wasmeasured in a thermostat of 150° C. The resistance increase rate of eachof the pastes was 20% or less and the resistance change rate sufficientto display the PTC function was not obtained.

Next, an electrolytic capacitor was manufactured by using theelectrolytic capacitor manufacturing method of the third embodiment. Aprocedure of manufacturing an electrolytic capacitor (including aprocedure of forming a solid electrolyte layer) is similar to that ofthe case of manufacturing the electrolytic capacitor of the secondembodiment except for the point that the cathode is formed so as to havea two-layer structure of the sub and main electrode layers.

Electrolytic capacitors (Examples 3-1 to 3-6) of the invention weremanufactured while changing the configuration of the cathode (subelectrode layer and main electrode layer) having the PTC function byusing the electrolytic capacitor manufacturing method and, after that,the characteristics of the electrolytic capacitors were examined. At thetime of examining the characteristics of the electrolytic capacitors ofthe invention, to compare and evaluate the performances, comparativeelectrolytic capacitors (Comparative Examples 3-1 to 3-3) were alsomanufactured while changing the configuration of the cathode and thecharacteristics of the electrolytic capacitors were also examined.

Example 3-1

A cathode was formed by the following procedure so that only a mainelectrode layer has the PTC function. Specifically, carbon black (CB)paste TC-8263 of Tanaka Kikinzoku Kogyo K. K. was used as the material(carbon paste) of a sub electrode layer. The carbon paste was applied onthe surface of a solid electrolyte layer and dried at 125° C., therebyforming the sub electrode layer. As the material (metal paste) of themain electrode layer, a thermosetting high polymer as a liquid highpolymer (film high polymer), concretely, a mixture (epoxy resin α:mixing weight ratio of (EPICLON850: EP4005)=75:25) between an epoxyresin EPICLON850 (epoxy equivalent=190 g/eq) of Dainippon Ink andChemicals, Incorporated and an epoxy resin EP4005 (epoxy equivalent=510g/eq) of Asahi Denka Co., Ltd. was used. As the conductive particles,filament nickel powders Type 255 (Niα; average particle diameter=2.2 μmto 2.8 μm, apparent density=0.50 g/cm³ to 0.65 g/cm³, specific surfacearea=0.68 m²/g, addition capacity ratio (high polymer: conductiveparticles)=40:60) of INCO Limited were used. A metal paste was appliedon the surface of the main electrode layer and was set at 130° C. undernitrogen atmosphere, thereby forming a main electrode layer so as tohave the thickness of 0.2 mm. As the metal paste, a metal pastecontaining the liquid high polymer and conductive particles and, as aco-hardener, a hardener B570 (acid anhydride equivalent=168 g/eq,equivalent ratio between acid anhydride and liquid high polymer=1:1) ofDainippon Ink and Chemicals, Incorporated and a hardening acceleratorPN-40J (addition amount=1% by weight of the weight of the liquid highpolymer) of Ajinomoto-Fine-Techno Co., Inc. was used.

Example 3-2

A cathode was formed by a procedure similar to that of Example 3-1except for the point that silver-coated nickel flakes (Niβ; silvercoating ratio=15%, apparent density=2.4 g/cc, addition capacity ratio(liquid high polymer: conductive particles)=45:55) of Novamet SpecialtyProducts Corporation were used.

Example 3-3

A cathode was formed by a procedure similar to that of Example 3-1except for the point that a main electrode layer was formed so as tohave a thickness of 0.2 μm by using, as the material (metal paste) ofthe main electrode layer, a soluble thermoplastic high polymer as aliquid high polymer (film high polymer), concretely, polyvinylidenefluoride (PVDF) Kynar7201 (melting point=122° C. to 126° C., specificgravity=1.88) of Atofina Chemicals dissolved in a mixture solvent ofacetone and toluene, using, as the conductive particles, tungstencarbide (WC) WC-F (particle diameter=0.62 μm, addition capacity ratio(liquid high polymer: conductive particles)=70:30) of Japan New MetalsCo., Ltd., applying a metal paste prepared by stirring the conductiveparticles in the liquid high polymer by a ball mill onto the surface ofa sub electrode layer, and drying the resultant in vacuum at 100° C.

Example 3-4

A cathode was formed so that only the sub electrode layer has the PTCfunction by the following procedure. As the material (carbon paste) ofthe sub electrode layer, a thermosetting high polymer as a liquid highpolymer (film high polymer), concretely, the epoxy resin α (containingthe co-hardener (the hardener and the hardening accelerator)) used inExample 3-1 was used. As the conductive particles, carbon black (CB)#4500 TOKABLACK (particle diameter=40 nm, DBP absorption number=168cc/100 g, specific surface area=58 m²/g, addition capacity ratio (liquidhigh polymer: conductive particles)=67:33) of Tokai Carbon Co., Ltd wasused. A mixture obtained by mixing and stirring the liquid high polymerand the conductive particles was applied on the surface of the solidelectrolyte layer and was set at 130° C. under nitrogen atmosphere,thereby forming the sub electrode layer. As the material (metal paste)of the main electrode layer, silver paste NH-1429N of Tanaka KikinzokuKogyo K. K. was used. The silver paste was applied on the surface of thesub electrode layer and dried, thereby forming the main electrode layer.

Example 3-5

A cathode was formed by a procedure similar to that of Example 3-4except for the point that a thermosetting high polymer as the liquidhigh polymer (film high polymer), concretely, an epoxy resin AK-601(epoxy resin β; epoxy equivalent=153 g/eq) of Nippon Kayaku Co., Ltd.was used.

Example 3-6

A cathode was formed by a procedure similar to that of Example 3-4except for the point that polyvinylidene fluoride (PVDF; PVDF dissolvedin a mixture solvent of acetone and toluene) used as a liquid highpolymer (film high polymer) in Example 3-3 was used as the material(carbon paste) of the sub electrode layer, the carbon black used inExample 3-4 was used as conductive particles, and a carbon pasteprepared by stirring the conductive particles in the liquid high polymerby a ball mill was applied onto the surface of a solid electrolyte layerand dried in vacuum at 100° C., thereby forming a sub electrode layer.

Comparative Example 3-1

A cathode was formed by a procedure similar to that of Example 3-1except for the point that a silver paste (without the PTC function) usedin Example 3-4 was used as the material (metal paste) of the mainelectrode layer and the metal paste was applied on the surface of thesub electrode layer and dried, thereby forming the main electrode layerwithout the PTC function.

Comparative Example 3-2

A cathode was formed by a procedure similar to that of Example 3-1except for the point that a thermoplastic conductive high polymer sheetwas thermo-compression-bonded as a main electrode layer to the subelectrode layer without using the metal paste as the material of themain electrode layer. At the time of forming the conductive high polymersheet, an insoluble thermoplastic high polymer, concretely, high densitypolyethylene (HDPE) HY540 (melting point=135° C. and specificgravity=0.961) of Japan Polyethylene Corporation was used. As theconductive particles, filament nickel powder type 210 (average particlediameter=0.5 μm to 1.0 μm, apparent density=0.80 g/cm³, specific surfacearea=1.50 m²/g to 2.50 m²/g, addition capacity ratio (high polymer:conductive particles)=65:35) of INCO Limited was used. The high polymerand conductive particles were melted and kneaded in a kneading mill of150° C. The kneaded material was thermal-pressed so as to be formed in asheet shape. At the time of thermo-compression-bonding the conductivehigh polymer sheet to the sub electrode layer, the conductive highpolymer sheet was thermal-pressed to the sub electrode layer at 150° C.

Comparative Example 3-3

A cathode was formed by a procedure similar to that of Example 3-4except for the point that a thermoplastic conductive high polymer sheetwas thermo-compression-bonded as a sub electrode layer to the solidelectrolyte layer without using the carbon paste as the material of thesub electrode layer. At the time of forming the high polymer sheet, aninsoluble thermoplastic high polymer, concretely, high densitypolyethylene (HDPE) used in Comparative Example 3-2 was used. As theconductive particles, the carbon black used in Example 3-4 was used. Thehigh polymer and conductive particles were melted and kneaded in akneading mill of 150° C. The kneaded material was thermal-pressed so asto be formed in a sheet shape. At the time of thermo-compression-bondingthe high polymer sheet to the sub electrode layer, the high polymersheet was thermal-pressed to the sub electrode layer at 150° C.

The characteristics of the electrolytic capacitors of Examples 3-1 to3-6 and Comparative Examples 3-1 to 3-3 were examined and the resultshown in Tables 4 and 5 was obtained.

The characteristics of the electrolytic capacitors of Examples 3-1 to3-3 and Comparative Examples 3-1 and 3-2 were examined and the resultshown in Table 4 was obtained. Table 4 shows the characteristics of theelectrolytic capacitors, which are “ESR (Equivalent Series ResistancemΩ)”, “leak current (μA)”, and “backward voltage test”. For referencesake, in Table 4, the materials (the liquid high polymer (film highpolymer) and conductive particles) of the sub and main electrode layers,and the presence/absence of the PTC function are also shown.

TABLE 4 Main electrode layer (with PTC function) Leak Backward Subelectrode layer Liquid high polymer Conductive ESR current voltage(without PTC function) (film high polymer) particles (mΩ) (μA) testExample 3-1 CB paste Epoxy resin α Ni α 48 3.6 Good Example 3-2 CB pasteEpoxy resin α Ni β 51 4.3 Good Example 3-3 CB paste PVDF WC 45 3.5 GoodComparative CB paste Silver paste (without PTC function) 35 1.2 Badexample 3-1 Comparative CB paste Conductive high polymer sheet 142 536.0Good example 3-2

As understood from Table 4, if conditions (suitable conditions) suchthat the ESR is 100 mΩ or less, leak current is 10.0 μA or less, and thebackward voltage test is “good” have to be satisfied as characteristicsfor practical use of an electrolytic capacitor, the electrolyticcapacitors of Examples 3-1 to 3-3 satisfy the suitable conditions of allof the ESR, leak current, and backward voltage test. Specifically,firing, smoke, and the like did not occur in the electrolytic capacitorsof Examples 3-1 to 3-3 for the reasons: (1) since the carbon paste andmetal paste are applied to form a film to thereby form a cathode (subelectrode layer and main electrode layer), the contact resistancebetween the solid electrolyte layer and the cathode decreases so thatthe ESR is reduced, (2) since excessive external force is not applied tothe dielectric layer at the time of forming the cathode because the mainelectrode layer is not thermo-compression-bonded to the sub electrodelayer, the dielectric layer is not broken due to a mechanical factorduring manufacture and, accordingly, leak current is suppressed, and (3)although excess current flows instantaneously when backward voltage isapplied, the resistance of the cathode is increased by using the PTCfunction of the main electrode layer, and excess current is suppressed.On the other hand, the electrolytic capacitors of Comparative Examples3-1 and 3-2 do not satisfy part of the suitable conditions of the ESR,leak current, and backward voltage test. Concretely, the electrolyticcapacitor of Comparative Example 3-1 satisfies the suitable conditionsof both of the ESR and leak current but does not satisfy the backwardvoltage test. The electrolytic capacitor of Comparative Example 3-2satisfies the suitable condition of the backward voltage test but doesnot satisfy the suitable conditions of the ESR and leak current.Specifically, in the electrolytic capacitor of Comparative Example 3-1,a cathode is formed by applying the carbon paste and metal paste and themain electrode layer is not thermo-compression-bonded to the subelectrode layer. Consequently, in a manner similar to Examples 3-1 to3-3, the ESR and leak current are reduced. However, the cathode does nothave the PTC function, so that smoke was generated in the backwardvoltage test. In the electrolytic capacitor of Comparative Example 3-2,the main electrode layer was formed by thermo-compression-bonding theconductive high polymer sheet having the PTC function, so that no fireor smoke occurred in the backward voltage test. However, the ESR becamevery high due to increase in the contact resistance between the solidelectrolyte layer and the cathode, and the dielectric layer was severelydamaged due to an excessive external force at the time of thermocompression bonding, so that leak current increased remarkably. It wasconsequently recognized that in the electrolytic capacitors of Examples3-1 to 3-3, both of the ESR and leak current are suppressed andoccurrence of a trouble such as firing and smoke is prevented, so thatthe electrolytic capacitors can be stably manufactured.

The characteristics of the electrolytic capacitors of Examples 3-4 to3-6 and Comparative Example 3-3 were examined and the result shown inTable 5 was obtained. Table 5 shows the characteristics of theelectrolytic capacitors and shows, as the characteristics, like Table 4,the characteristics of “ESR (mΩ)”, “leak current (μA)”, and “backwardvoltage test” and, in addition, the materials of the sub and mainelectrode layers, and the presence/absence of the PTC function.

TABLE 5 Sub electrode layer (with PTC function) Liquid Leak high polymerConductive Main electrode layer ESR current Backward (film high polymer)particles (without PTC function) (mΩ) (μA) voltage test Example 3-4Epoxy resin α CB Silver paste 72 2.1 Good Example 3-5 Epoxy resin β CBSilver paste 69 3.2 Good Example 3-6 PVDF CB Silver paste 68 4.4 GoodComparative Conductive high polymer sheet Silver paste 197 897.0 Goodexample 3-3

As understood from Table 5, if suitable conditions (ESR≦100, leakcurrent≧10.0 μA, and the backward voltage test=“good”) regardingcharacteristics for practical use of an electrolytic capacitor areconsidered, the electrolytic capacitors of Examples 3-4 to 3-6 satisfythe suitable conditions of all of the ESR, leak current, and backwardvoltage test for reasons similar to those of the electrolytic capacitorsof Examples 3-1 to 3-3. In contrast, in the electrolytic capacitor ofComparative Example 3-3, for reasons similar to those of theelectrolytic capacitor of Comparative Example 3-2, firing, smoke, andthe like did not occur in the backward voltage test, but both of the ESRand leak current largely increased. It was consequently recognized thatalso in the electrolytic capacitors of Examples 3-4 to 3-6, both of theESR and leak current are suppressed and occurrence of a trouble such asfiring and smoke is prevented, so that the electrolytic capacitors canbe stably manufactured.

Although concrete data will not be presented, the characteristics of theelectrolytic capacitor manufactured so that both of the sub and mainelectrode layers have the PTC function, concretely, the electrolyticcapacitors obtained by replacing the sub electrode layers (without thePTC function) of Examples 3-1 to 3-3 with the sub electrode layers (withthe PTC function) of Examples 3-4 to 3-6, and he electrolytic capacitorsobtained by replacing the main electrode layers (with the PTC function)of Examples 3-4 to 3-6 with the sub electrode layers (with the PTCfunction) of Examples 3-1 to 3-3 were examined, and results similar tothose obtained with respect to the electrolytic capacitors of Examples3-1 to 3-6 were obtained in each of the electrolytic capacitors. Thus,it was recognized that, also in the case where both of the sub and mainelectrode layers are provided with the PTC function, the electrolyticcapacitor can be stably manufactured.

For reference sake, the PTC characteristics of the cathodes of Examples3-1 to 3-6 and Comparative Examples 3-2 to 3-3 were examined and resultsshown in Table 6 were obtained. Table 6 shows the PTC characteristics ofthe cathodes. As the PTC characteristics, “room temperature resistance(mΩ)”, “operation start temperature (° C.)”, and “resistance change rate(the number of digits)” are shown. At the time of examining the PTCfunctions, with respect to Examples 3-1 to 3-3 in which the mainelectrode layer has the PTC function, a film was formed by using thematerial (metal paste) of the main electrode layer so as to have athickness of 0.2 mm between two electrolytic nickel foil electrodes(having a thickness of 25 μm), thereby forming a PTC sheet with anelectrode. The PTC sheet was punched in a disc shape having a diameterof 10 mm. After that, the PTC sheet with an electrode was put in athermostat and resistance was measured at every two degrees by afour-terminal method while increasing the temperature at 2° C./min.within the range from 25° C. to 160° C. With respect to Examples 3-4 to3-6 in which the sub electrode layer has the PTC function, a PTC sheetwith an electrode was manufactured by a procedure similar to that ofExamples 3-1 to 3-3 except for the point that the material (carbonpaste) of the sub electrode layer is used, and resistance of the PTCsheet with the electrode was measured. Further, with respect toComparative Examples 3-2 and 3-3 in which the conductive high polymersheet has the PTC function, a PTC sheet with an electrode wasmanufactured by a procedure similar to that of Examples 3-1 to 3-3 orExamples 3-4 to 3-6 except for the point that the conductive highpolymer sheet was thermo-compression-bonded between two electrolyticnickel foil electrodes, and resistance of the PTC sheet with theelectrode was measured. For reference, Table 6 also shows the kind of anelectrode layer to be measured in the cathode, that is, the electrodelayer with the PTC function.

TABLE 6 Measured Operation start Resistance change electrode layerResistance (mΩ) at temperature rate (with PTC function) room temperature(° C.) (the number of digits) Example 3-1 Main electrode layer 1.2 1255.5 Example 3-2 Main electrode layer 2.4 123 5.1 Example 3-3 Mainelectrode layer 1.5 117 8.2 Example 3-4 Sub electrode layer 30.2 123 3.8Example 3-5 Sub electrode layer 32.5 120 3.7 Example 3-6 Sub electrodelayer 30.7 128 5.3 Comparative Main electrode layer 0.7 127 9.0 example3-2 Comparative Sub electrode layer 27.2 126 5.2 example 3-3

As understood from the results shown in Table 6, in all of the cathodesof Examples 3-1 to 3-6 and Comparative Examples 3-2 and 3-3, theresistance change rate of three or more digits is obtained, that is, theresistance increased by 1,000 times or more. Consequently, it wasrecognized that the cathodes of Examples 3-1 to 3-6 and ComparativeExamples 3-2 to 3-3 have the resistance change rate sufficient todisplay the PTC function.

Finally, an electrolytic capacitor was manufactured by using theelectrolytic capacitor manufacturing method of the fourth embodiment. Bya procedure similar to the procedure of manufacturing an electrolyticcapacitor (including a procedure of forming a solid electrolyte layer)of the third embodiment, a capacitor element was formed. A procedure offorming a solid electrolyte layer is similar to that of the case ofmanufacturing the electrolytic capacitor of the third embodiment. A PTClayer having a sheet structure was prepared by forming a sheet by usinga high polymer containing conductive particles, surface process forexposing the conductive particles was performed on the bottom face (facefacing the cathode) of the PTC layer, and the bottom face of the PTClayer was bonded to the cathode by using a conductive adhesive, therebyconnecting the PTC layer to the cathode via the conductive adhesive.Subsequently, an anode lead made of copper was connected to the anode inthe capacitor element by using a conductive adhesive and, similarly, acathode lead made of copper was bonded to the PTC layer by using aconductive adhesive. Finally, the periphery of the capacitor element wascovered with an epoxy resin as a mold resin so that the anode andcathode leads are partially exposed, thereby completing the electrolyticcapacitor. As the conductive adhesive, a conductive adhesive DotiteXA-874 of Fujikurakasei Co., Ltd was used.

Electrolytic capacitors (Examples 4-1 to 4-5) of the invention weremanufactured while changing the configuration of the PTC layer havingthe PTC function by using the electrolytic capacitor manufacturingmethod and, after that, the characteristics of the electrolyticcapacitors were examined. At the time of examining the characteristicsof the electrolytic capacitors of the invention, to compare and evaluatethe performances, comparative electrolytic capacitors (ComparativeExamples 4-1 to 4-4) were also manufactured while changing theconfiguration of the PTC layer as follows, and the electrolyticcapacitor (Comparative Example 4-5) was also manufactured so as not tohave the PTC layer, and the characteristics of the electrolyticcapacitors were also examined.

Example 4-1

A PTC layer was formed by the following procedure and the surfaceprocess was performed on the PTC layer, thereby manufacturing anelectrolytic capacitor. As a procedure of preparing the PTC layer, amixture (mixing weight ratio of (EPICLON850: EP4005)=75:25) between anepoxy resin EPICLON850 (epoxy equivalent =190 g/eq) of Dainippon Ink andChemicals, Incorporated and an epoxy resin EP4005 (epoxy equivalent=510g/eq) of Asahi Denka Co., Ltd. was used. As the conductive particles,metal particles, concretely, filament nickel powders (Ni) Type 255 (Niα;average particle diameter=2.2 μm to 2.8 μm, apparent density=0.50 g/cm³to 0.65 g/cm³, specific surface area=0.68 m²/g, addition capacity ratio(high polymer: conductive particles)=40:60) of INCO Limited were used.The high polymer and conductive particles were mixed and stirred and theresultant was applied on the surface of a PET (Polyethylen trephthalate)film and was set at 130° C. under nitrogen atmosphere, thereby forming asheet-shaped PTC layer so as to have the thickness of 0.2 mm. As thematerial of the PTC layer, a material containing not only the highpolymer and conductive particles but also, as a co-hardener, a hardenerB570 (acid anhydride equivalent=168 g/eq, equivalent ratio between acidanhydride and liquid high polymer=1:1) of Dainippon Ink and Chemicals,Incorporated and a hardening accelerator PN-40J (addition amount=1% byweight of the weight of the liquid high polymer) ofAjinomoto-Fine-Techno Co., Inc. was used. An ozone process as thesurface process was performed on the PTC layer. Concretely, the UV ozonecleaner VUM-3073-13-00 manufactured by OAK Science Incorporation wasused to irradiate the bottom face of the PTC layer in the ozoneatmosphere with ultraviolet rays for three minutes, thereby partiallyremoving the high polymer so that the removal depth becomes about 5 μmand forming a recess.

Example 4-2

An electrolytic capacitor was manufactured by a procedure similar tothat of Example 4-1 except for the point that a plasma process was usedin place of the ozone process as the surface process on the PTC layer.Concretely, an ashing system of a reactive ion etching type using oxygen(O₂) as the discharge gas was used to etch the bottom face of the PTClayer under conditions of pressure=20 Pa, power density=0.25 W/cm³, andprocess time=1 minute.

Example 4-3

An electrolytic capacitor was manufactured by a procedure similar tothat of Example 4-1 except for the point that polyvinylidene fluoride(PVDF) Kynar7201 (melting point=122° C. to 126° C., specificgravity=1.88) of Atofina Chemicals was used as a high polymer,conductive ceramic particles, concretely, tungsten carbide (WC) WC-F ofJapan New Metals Co., Ltd. (particle diameter=0.62 μm and additioncapacity ratio (liquid high polymer: conductive particles)=70:30) wasused as the conductive particles, a paste prepared by stirring theconductive particles in the high polymer dissolved in a mixture solventof acetone and toluene by a ball mill was applied on the surface of aPET film and dried in vacuum at 100° C., thereby forming a PTC layer ina sheet shape so as to have a thickness of 0.2 mm, and the high polymerwas partially removed under conditions of ultraviolet irradiation timeof 5 minutes and removal depth of 2 μm.

Example 4-4

An electrolytic capacitor was manufactured by a procedure similar tothat of Example 4-1 except for the point that linear low-densitypolyethylene (L-LDPE) UJ960 (melting point=127° C. and specificgravity=0.921) of Japan Polyethylene Corporation was used as the highpolymer, metal particles, concretely, filament nickel powder (Ni) type210 (Niβ; average particle diameter=0.5 μm to 1.0 μm, apparentdensity=0.80 g/cm³, specific surface area=1.50 m²/g to 2.00 m²/g,addition capacity ratio (high polymer: conductive particles)=65:35) ofINCO Limited was used as the conductive particles, the high polymer andconductive particles were melted and kneaded in a kneading mill of 150°C., and the kneaded material was thermal-pressed andelectron-beam-bridged with a doze of 100 kGy (gray), thereby forming asheet-shaped PTC layer so as to have a thickness of 0.2 mm, and the highpolymer was partially removed under conditions of ultravioletirradiation time of 3 minutes and removal depth of 3 μm.

An electrolytic capacitor was manufactured by a procedure similar tothat of Example 4-1 except for the point that high density polyethylene(HDPE) HY540 (melting point=135° C., specific gravity=0.961) of JapanPolyethylene Corporation was used as the high polymer, carbon particles,concretely, carbon black (CB) #4500 TOKABLACK (particle diameter =40 nm,DBP absorption number=168 cc/100 g, specific surface area=58 m²/g,addition capacity ratio (high polymer: conductive particles)=68:32) ofTokai Carbon Co., Ltd. was used as conductive particles, the highpolymer and conductive particles were melted and kneaded in a kneadingmill of 150° C., and the kneaded material was thermal-pressed andelectron-beam-bridged with a doze of 100 kGy (gray), thereby forming asheet-shaped PTC layer so as to have a thickness of 0.2 mm, and the highpolymer was partially removed under conditions of ultravioletirradiation time of 1 minute and removal depth of 1 μm.

Comparative Example 4-1

An electrolytic capacitor was manufactured by a procedure similar tothose of Examples 4-1 and 4-2 except that the surface process is notperformed on the bottom face of the PTC layer

Comparative Example 4-2

An electrolytic capacitor was manufactured by a procedure similar tothat of Example 4-3 except that the surface process is not performed onthe bottom face of the PTC layer

Comparative Example 4-3

An electrolytic capacitor was manufactured by a procedure similar tothose of Example 4-4 except that the surface process is not performed onthe bottom face of the PTC layer.

Comparative Example 4-4

An electrolytic capacitor was manufactured by a procedure similar tothose of Example 4-5 except that the surface process is not performed onthe bottom face of the PTC layer.

Comparative Example 4-5 For reference sake, an electrolytic capacitorwas manufactured without a PTC layer, that is, so as not to provide thePTC function.

The characteristics of the electrolytic capacitors of Examples 4-1 to4-5 and Comparative Examples 4-1 to 4-5 were examined and the resultsshown in Tables 7 to 10 were obtained. Tables 7 to 10 show thecharacteristics of the electrolytic capacitors, which are “ESR(Equivalent Series Resistance mΩ)”, “leak current (μA)”, and “backwardvoltage test”. Table 7 shows the characteristics of the electrolyticcapacitors of Examples 4-1 and 4-2 and Comparative Example 4-1. Table 8shows the characteristics of the electrolytic capacitors of Example 4-3and Comparative Example 4-2. Table 9 shows the characteristics of theelectrolytic capacitors of Example 4-4 and Comparative Example 4-3.Table 10 shows the characteristics of the electrolytic capacitors ofExample 4-5 and Comparative Example 4-4. For reference sake, in all ofTables 7 to 10, the characteristics of the electrolytic capacitor ofComparative Example 4-5 are also shown. In Tables 7 to 10, for referencesake, in addition to the materials (the high polymer and conductiveparticles) of the PTC layer, the presence/absence of the PTC function,the PTC layer forming method, and the surface process are also shown.

TABLE 7 Leak High Conductive PTC Surface ESR current Backward polymerparticles function Forming method process (mΩ) (μA) voltage test Example4-1 Epoxy Ni α Presence Coating/thermo Presence 40.2 3.1 Good resincompression bonding (ozone) Example 4-2 Epoxy Ni α PresenceCoating/thermo Presence 39.9 3.8 Good resin compression bonding(etching) Comparative Epoxy Ni α Presence Coating/thermo Absence 48.83.5 Good example 4-1 resin compression bonding Comparative — — Absence —Absence 35.0 1.2 Bad example 4-5

TABLE 8 Leak High Conductive Forming Surface ESR current Backwardpolymer particles PTC function method process (mΩ) (μA) voltage testExample 4-3 PVDF WC Presence Coating/drying Presence 49.4 2.6 Good(ozone) Comparative PVDF WC Presence Coating/drying Absence 56.2 3.1Good example 4-2 Comparative — — Absence — Absence 35.0 1.2 Bad example4-5

TABLE 9 Leak High Conductive PTC Forming Surface ESR current Backwardpolymer particles function method process (mΩ) (μA) voltage test Example4-4 L-LDPE Ni β Presence Thermal Presence 39.5 3.4 Good press (ozone)Comparative L-LDPE Ni β Presence Thermal Absence 74.4 4.9 Good example4-3 press Comparative — — Absence — Absence 35.0 1.2 Bad example 4-5

TABLE 10 Leak High Conductive PTC Forming Surface ESR current Backwardpolymer particles function method process (mΩ) (μA) voltage test Example4-5 HDPE CB Presence Thermal Presence 71.6 5.1 Good press (ozone)Comparative HDPE CB Presence Thermal Absence 162.0 5.8 Good example 4-4press Comparative — — Absence — Absence 35.0 1.2 Bad example 4-5

As understood from Table 7, when the characteristics of the electrolyticcapacitors of Examples 4-1 and 4-2 in which the surface process isperformed on the PTC layer are compared with those of the electrolyticcapacitor of Comparative Example 4-1 in which the surface process is notperformed on the PTC layer, firing, smoke, and the like did not occur inthe electrolytic capacitors of Examples 4-1 and 4-2 and the electrolyticcapacitor of Comparative Example 4-1 since the PTC layer having the PTCfunction is provided. The leak current in the electrolytic capacitors ofExamples 4-1 and 4-2 and that in the electrolytic capacitor ofComparative Example 4-1 are almost the same. However, the ESR in theelectrolytic capacitors of Examples 4-1 and 4-2 is lower than that ofthe electrolytic capacitor of Comparative Example 4-1. Specifically, inthe electrolytic capacitors of Examples 4-1 and 4-2, the surface processis performed on the bottom face of the PTC layer so that the conductiveparticles are exposed. Consequently, the contact resistance between thePTC layer and the cathode decreases and, as a result, the ESR islowered. Therefore, in the electrolytic capacitors of Examples 4-1 and4-2, both of the ESR and leak current are suppressed, occurrence of atrouble such as firing, smoke, and the like is prevented and,particularly, it was recognized that the resistance characteristic ofthe electrolytic capacitors can be reduced. For reference sake, thecharacteristics of the electrolytic capacitors of Examples 4-1 and 4-2having the PTC layer and those of the electrolytic capacitor ofComparative Example 4-5 having no PTC layer were examined. The ESR andleak current of the electrolytic capacitor of Comparative Example 4-5are almost the same as those of the electrolytic capacitors of Examples4-1 and 4-2. However, different from the electrolytic capacitors ofExamples 4-1 and 4-2, the PTC function is not provided, so that smokeoccurred in the backward voltage test.

As understood from the result shown in Table 8, when the characteristicsof the electrolytic capacitor of Example 4-3 in which the surfaceprocess is performed on the PTC layer are compared with those of theelectrolytic capacitor of Comparative Example 4-2 in which the surfaceprocess is not performed on the PTC layer, like the result shown inTable 7, the results of leak current and backward voltage test of theelectrolytic capacitor of Example 4-3 and those of the electrolyticcapacitor of Comparative Example 4-2 are almost the same. However, theESR of the electrolytic capacitor of Example 4-3 is lower than that ofthe electrolytic capacitor of Comparative Example 4-2. Consequently,also in the electrolytic capacitor of Example 4-3, both of the ESR andthe leak current are suppressed, and occurrence of a trouble such asfiring or smoke is prevented. It was consequentially recognized that theresistance characteristic can be lowered.

As understood from the result shown in Table 9, when the characteristicsof the electrolytic capacitor of Example 4-4 in which the surfaceprocess is performed on the PTC layer are compared with those of theelectrolytic capacitor of Comparative Example 4-3 in which the surfaceprocess is not performed on the PTC layer, like the result shown inTable 7, the results of leak current and backward voltage test of theelectrolytic capacitor of Example 4-4 and those of the electrolyticcapacitor of Comparative Example 4-3 are almost the same. However, theESR of the electrolytic capacitor of Example 4-3 is lower than that ofthe electrolytic capacitor of Comparative Example 4-4. Consequently,also in the electrolytic capacitor of Example 4-4, both of the ESR andthe leak current are suppressed, and occurrence of a trouble such asfiring or smoke is prevented. It was consequentially recognized that theresistance characteristic can be lowered.

Further, as understood from the result shown in Table 10, when thecharacteristics of the electrolytic capacitor of Example 4-5 in whichthe surface process is performed on the PTC layer are compared withthose of the electrolytic capacitor of Comparative Example 4-4 in whichthe surface process is not performed on the PTC layer, like the resultshown in Table 7, the results of leak current and backward voltage testof the electrolytic capacitor of Example 4-5 and those of theelectrolytic capacitor of Comparative Example 4-4 are almost the same.However, the ESR of the electrolytic capacitor of Example 4-5 is lowerthan that of the electrolytic capacitor of Comparative Example 4-4.Consequently, also in the electrolytic capacitor of Example 4-5, both ofthe ESR and the leak current are suppressed, and occurrence of a troublesuch as firing or smoke is prevented. It was consequentially recognizedthat the resistance characteristic can be lowered.

As described above, in any of the electrolytic capacitors of theinvention (Examples 4-1 to 4-5), the resistance characteristic can belowered. In particular, when the ESR of the electrolytic capacitors ofthe invention were compared with each other, it was recognized that theESR in the electrolytic capacitors of Examples 4-1 to 4-4 using themetal particles or conductive ceramic particles as the conductiveparticles can be lowered more than the electrolytic capacitor of Example4-5 using the carbon particles as the conductive particles.

Although concrete data will not be presented, when electrolyticcapacitors were manufactured by performing an ultraviolet process and alaser process in place of the plasma process and the ozone process asthe surface process on the bottom face of the PTC layer and thecharacteristics were similarly examined, results similar to those of theelectrolytic capacitors of Examples 4-1 to 4-5 were obtained in any ofthe manufactured electrolytic capacitors. It was therefore recognizedthat the resistance characteristic of an electrolytic capacitor can belowered by performing the surface process for exposing the conductiveparticles on the bottom face of the PTC layer irrespective of the kindof the surface process.

Although concrete data will not be presented, when an electrolyticcapacitor in which the surface process is performed on only the top faceof the PTC layer and an electrolytic capacitor in which the surfaceprocess is performed on both of the top and bottom faces of the PTClayer were manufactured in place of the electrolytic capacitor in whichthe surface process is performed on only the bottom face of the PTClayer and the characteristics were similarly examined, results similarto those of the electrolytic capacitors of Examples 4-1 to 4-5 wereobtained also in any of the manufactured electrolytic capacitors. It wastherefore recognized that the resistance characteristic of anelectrolytic capacitor can be lowered by performing the surface processon the PTC layer.

For reference sake, the PTC characteristics of the PTC layers ofExamples 4-1 to 4-5 and Comparative Examples 4-1 to 4-4 were examinedand the results shown in Table 11 were obtained. Table 11 shows the PTCcharacteristics of the PTC layer. As the PTC characteristics, “roomtemperature resistance (mΩ)”, “operation start temperature (° C.)”, and“resistance change rate (the number of digits)” are shown. In the caseof examining the PTC characteristics, with respect to Examples 4-1 to4-3 and comparative examples 4-1 and 4-2, a film was formed by using thematerial (high polymer containing conductive particles) of the PTC so asto have a thickness of 0.2 mm between two electrolytic nickel foilelectrodes (having a thickness of 25 μm), thereby forming a PTC sheetwith an electrode. The PTC sheet was punched in a disc shape having adiameter of 10 mm. After that, the PTC sheet with an electrode was putin a thermostat and resistance was measured at every two degrees by afour-terminal method while increasing the temperature at 2° C./min.within the range from 25° C. to 160° C. With respect to Examples 4-4 and4-5 and Comparative Examples 4-3 and 4-4, a PTC sheet with an electrodewas manufactured by a procedure similar to that of Examples 4-1 to 4-3and Comparative Examples 4-1 and 4-2 except for the point that the PTClayer was thermo-compression-bonded between two electrolytic nickel foilelectrodes, and resistance of the PTC sheet with the electrode wasmeasured.

TABLE 11 Resistance (mΩ) Operation Resistance change rate at roomtemperature start temperature (° C.) (the number of digits) Examples 4-1and 4-2 1.2 125 5.5 Comparative example 4-1 Example 4-3 1.5 117 8.2Comparative example 4-2 Example 4-4 1.1 115 8.7 Comparative example 4-3Example 4-5 27.2 126 5.2 Comparative example 4-4

As understood from the results shown in Table 11, in all of the PTClayers of Examples 4-1 to 4-5 and Comparative Examples 4-1 to 4-4, theresistance change rate of three or more digits is obtained, that is, theresistance increased by 1,000 times or more. Consequently, it wasrecognized that the PTC layers of Examples 4-1 to 4-5 and ComparativeExamples 4-1 to 4-4 have the resistance change rate sufficient todisplay the PTC function.

Although the invention has been described by the embodiments andexamples, the invention is not limited to the embodiments and examples.As long as an electrolytic capacitor can be constructed or manufacturedso as to have the PTC function, the configuration, material, anddimensions of the electrolytic capacitor, the procedure of manufacturingthe electrolytic capacitor, and the like can be freely changed.

The electrolytic capacitor according to the invention and the method ofmanufacturing the same can be applied to a solid electrolytic capacitorwhose main part (capacitor element) in which electric reaction occurs isconstructed by containing a solid material (conductive high polymer).

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

1. An electrolytic capacitor having a stacked structure in which a firstelectrode layer, a dielectric layer, a solid electrolyte layer, and asecond electrode layer having a Positive Temperature Coefficientfunction in which resistance increases exponentially in accordance witha rise in temperature within a predetermined temperature range arestacked in this order.
 2. An electrolytic capacitor according to claim1, wherein the second electrode layer has a stacked structure in whichtwo or more layers are stacked and, in at least one of the two or morelayers, resistance increases in accordance with rise in temperaturewithin a predetermined temperature range.
 3. An electrolytic capacitoraccording to claim 2, wherein the second electrode layer has a two-layerstructure including a main electrode layer for assuring conductivity anda sub electrode layer which is disposed between the main electrode layerand the solid electrolyte layer and is used for electrically bonding themain electrode layer to the solid electrolyte layer.
 4. An electrolyticcapacitor according to claim 1, wherein the second electrode layer has asingle-layer structure.
 5. An electrolytic capacitor according to claim1, wherein the second electrode layer contains a high polymer andconductive particles held in the high polymer.
 6. An electrolyticcapacitor according to claim 1, wherein the second electrode layercontains at least one of metal particles and conductive ceramicparticles.
 7. An electrolytic capacitor according to claim 6, whereinthe second electrode layer has a stacked structure in which two or morelayers are stacked and, in at least one of the two or more layers, atleast one of the metal particles and the conductive ceramics particlesis contained and resistance increases in accordance with rise intemperature within a predetermined temperature range.
 8. An electrolyticcapacitor according to claim 7, wherein the second electrode layer has athree-layer structure comprising: a main electrode layer for assuringconductivity; a sub electrode layer which is disposed between the mainelectrode layer and the solid electrolyte layer and is used forelectrically bonding the main electrode layer to the solid electrolytelayer; and an auxiliary electrode layer which is disposed on the sideopposite to the sub electrode layer while sandwiching the main electrodelayer and contains at least one of the metal particles and theconductive ceramic particles, and whose resistance increases inaccordance with rise in temperature within a predetermined temperaturerange.
 9. An electrolytic capacitor according to claim 6, wherein thesecond electrode layer has a single-layer structure.
 10. An electrolyticcapacitor according to claim 6, wherein the metal particles are metalparticles of at least one of the group including nickel (Ni), copper(Cu), aluminum (Al), tungsten (W), molybdenum (Mo), zinc (Zn), cobalt(Co), platinum (Pt), gold (Au), and silver (Ag), and the conductiveceramic particles are conductive ceramic particles of at least one ofthe group including tungsten carbide (WC), titanium nitride (TiN),zirconium nitride (ZrN), titanium carbide (TiC), titanium boride (TiB₂),molybdenum silicide (MoSi₂), and tantalum boride (TaB₂).
 11. Anelectrolytic capacitor according to claim 6, wherein a material forincreasing the resistance in accordance with rise in the temperaturewithin a predetermined temperature range is a liquid high polymercontaining at least one of the metal particles and the conductiveceramic particles, and the second electrode layer contains a film-shapedhigh polymer formed by using the liquid high polymer and at least one ofthe metal particles and the conductive ceramic particles held in thefilm-shaped high polymer.
 12. The electrolytic capacitor according toclaim 1, wherein the second electrode layer is formed in a film shape byusing a liquid material for increasing resistance in accordance withrise in temperature within a predetermined temperature range on thesurface of the solid electrolyte layer.
 13. An electrolytic capacitoraccording to claim 12, wherein the second electrode layer has a stackedstructure in which two or more layers are stacked and, in at least oneof the two or more layers, resistance increases in accordance with risein temperature within a predetermined temperature range.
 14. Anelectrolytic capacitor according to claim 12, wherein the secondelectrode layer has a single-layer structure.
 15. An electrolyticcapacitor according to claim 12, wherein the liquid material is a liquidhigh polymer containing conductive particles, and the second electrodelayer contains a film-shaped high polymer formed by using the liquidhigh polymer and the conductive particles held in the film-shaped highpolymer.
 16. An electrolytic capacitor according to claim 1, wherein theresistance increases by about 1,000 times or more in the temperaturerange from about 60° C. or higher and 150° C. or lower.
 17. Anelectrolytic capacitor manufacturing method comprising the step offorming a second electrode layer having a Positive TemperatureCoefficient function in which resistance increases exponentially inaccordance with a rise in temperature within a predetermined temperaturerange on a solid electrolyte layer in a stacked structure in which afirst electrode layer, a dielectric layer, and the solid electrolytelayer are stacked in this order.
 18. An electrolytic capacitormanufacturing method according to claim 17, wherein the second electrodelayer is formed by containing at least one of metal particles orconductive ceramic particles.
 19. An electrolytic capacitormanufacturing method according to claim 17, wherein the second electrodelayer is formed by supplying a liquid material for increasing resistancein accordance with rise in temperature within a predeterminedtemperature range on the surface of the solid electrolyte layer.